Browsing by Author "Raghunath, P."

Now showing 1 - 20 of 39

A Computational Study on the Adsorption Configurations and Reactions of Phosphorous Acid on TiO(2) Anatase (101) and Rutile (110) Surfaces
(2009-05-14)
Raghunath, P.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
We report the result of a density functional theory study on the adsorption and decomposition pathways of phosphorous acid (H(3)PO(3)) on TiO(2) anatase (101) and rutile (110) surfaces. The most stable adsorption structure for H(3)PO(3) and its isomer, HP(O)(OH)(2), is a monodentate adsorption mode for the anatase surface with calculated adsorption energies 23.5 and 38.5 kcal/mol and a bidentate adsorption mode for rutile surface with 26.7 and 36.6 kcal/mol. The mechanisms for the surface reactions of these species have been explicitly elucidated with the computed potential energy surfaces. The barriers for the stepwise H(3)PO(3) H-migration to two nearby bridged O atoms reactions on anatase leads to Ti-OP(OH)O-Ti(a) + 2H-O(b)(a) with 7.9 and 6.8 kcal/mol barriers. Even lower activation barriers (1.3 and 2.9 kcal/mol) have been obtained on the rutile (110) surface for the same bond breaking modes. The intermediate Ti-OP(OH)O-Ti(a) thus formed on both surfaces can further decompose via two distinct pathways through H-migration to the P atom and H(2)O elimination to produce Ti-OP(H)(O)O-Ti(a) and Ti-OPO-Ti(a), respectively. In addition, we have calculated the adsorption and reactions of the dimer of H(3)PO(3) on both surfaces. The most noticeable difference occurs in the energy levels of the H(3)PO(3) reactions on the anatase and rutile surfaces, with the rutile being more reactive than the anatase surface. The predicted adsorption energies show that Ti-OP(OH)O-Ti(a) with two hydrogen atoms on bridged surface oxygen atoms is 47.1 kcal/mol for anatase and 42.4 kcal/mol for rutile; both are low when compared with the Ti-OB(OH)O-Ti(a) on the same surfaces, 140.1 and 134.6 kcal/mol, respectively. Our density of states analysis shows that OB(OH)O has a larger overlap with the TiO(2) surface than OP(OH)O has, favoring the former's charge transfer efficiency.
A Computational Study on the Adsorption Configurations and Reactions of Phosphorous Acid on TiO2 Anatase (101) and Rutile (110) Surfaces
(2009-05-14)
Raghunath, P.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
We report the result of a density functional theory study on the adsorption and decomposition pathways of phosphorous acid (H3PO3) on TiO2 anatase (101) and rutile (110) surfaces. The most stable adsorption structure for H3PO3 and its isomer, HP(O)(OH)(2), is a monodentate adsorption mode for the anatase surface with calculated adsorption energies 23.5 and 38.5 kcal/mol and a bidentate adsorption mode for rutile surface with 26.7 and 36.6 kcal/mol. The mechanisms for the surface reactions of these species have been explicitly elucidated with the computed potential energy surfaces. The barriers for the stepwise H3PO3 H-migration to two nearby bridged O atoms reactions on anatase leads to Ti-OP(OH)O-Ti(a) + 2H-O-b(a) with 7.9 and 6.8 kcal/mol barriers. Even lower activation barriers (1.3 and 2.9 kcal/mol) have been obtained on the rutile (110) surface for the same bond breaking modes. The intermediate Ti-OP(OH)O-Ti(a) thus formed on both surfaces can further decompose via two distinct pathways through H-migration to the P atom and H2O elimination to produce Ti-OP(H)(O)O-Ti(a) and Ti-OPO-Ti(a), respectively. In addition, we have calculated the adsorption and reactions of the dimer of H3PO3 on both surfaces. The most noticeable difference occurs in the energy levels of the H3PO3 reactions on the anatase and rutile surfaces, with the rutile being more reactive than the anatase surface. The predicted adsorption energies show that Ti-OP(OH)O-Ti(a) with two hydrogen atoms on bridged surface oxygen atoms is 47.1 kcal/mol for anatase and 42.4 kcal/mol for rutile; both are low when compared with the Ti-OB(OH)O-Ti(a) on the same surfaces, 140.1 and 134.6 kcal/mol, respectively. Our density of states analysis shows that OB(OH)O has a larger overlap with the TiO2 surface than OP(OH)O has, favoring the former's charge transfer efficiency.
A computational study on the adsorption configurations and reactions of SiHx(x=1-4) on clean and H-covered Si(100) surfaces
(2016-11-30)
Le, Thong N-M
;
Raghunath, P.
;
Huynh, Lam K.
;
Lin, M. C.
;
應用化學系
Possible adsorption configurations of H and SiHx (x= 1 4) on clean and H-covered Si(100) surfaces are determined by using spin-polarized DFT calculations. The results show that, on the clean surface, the gas-phase hydrogen atom and SiH3 radicals effectively adsorb on the top sites, while SiH and SiH2 prefer the bridge sites of the first layer. Another possibility for SiH is to reside on the hollow sites with a triple-bond configuration. For a partially H-coverd Si(100) surface, the mechanism is similar but with higher adsorption energies in most cases. This suggests that the surface species become more stable in the presence of surface hydrogens. The minimum energy paths for the adsorption/migration and reactions of H/SiHx species on the surfaces are explored using the climbing image-nudged elastic band method. The competitive surface processes for Si thin-film formation from SiHx precursors are also predicted. The study reveals that the migration of hydrogen adatom is unimportant with respect to leaving open surface sites because of its high barriers (>29.0 kcal/mol). Alternatively, the abstraction of hydrogen adatoms by H/SiHx radicals is more favorable. Moreover, the removal of hydrogen atoms from adsorbed SiHx, an essential step for forming Si layers, is dominated by abstraction rather than the decomposition processes. (C) 2016 Elsevier B.V. All rights reserved.
A computational study on the energetics and mechanisms for the dissociative adsorption of SiHx(x=1-4) on W(111) surface
(2016-01-30)
Lin, Y. H.
;
Raghunath, P.
;
Lin, M. C.
;
應用化學系
;
Department of Applied Chemistry
The adsorption and dissociation mechanisms of SiHx(x = 1-4) species on W(111) surface have been investigated by using the periodic density functional theory with the projector-augmented wave approach. The adsorption of all the species on four surface sites: top (T), bridge (B), shallow (S), and deep (D) sites have been analyzed. For SiH4 on a top site, T-SiH4(a), it is more stable with an adsorption energy of 2.6 kcal/mol. For SiH3, the 3-fold shallow site is most favorable with adsorption energy of 46.0 kcal/mol. For SiH2, its adsorption on a bridge site is most stable with 73.0 kcal/mol binding energy, whereas for SiH and Si the most stable adsorption configurations are on 3-fold deep sites with very high adsorption energies, 111.8 and 134.7 kcal/mol, respectively. The potential energy surfaces for the dissociative adsorption of all SiH species on the W(111) surface have been constructed using the CINEB method. The barriers for H-atom migration from SiHx(a) to its neighboring W atoms, preferentially on B-sites, were predicted to be 0.4, 1.0, 4.5 and, 8.0 kcal/mol, respectively, for x= 4, 3, 2, and 1, respectively. The adsorption energy of the H atom on a bridge site on the clean W(1 1 1) surface was predicted to be 65.9 kcal/mol, which was found to be slightly affected by the co-adsorption of SiHx-1 within +/- 1 kcal/mol. (C) 2015 Elsevier B.V. All rights reserved.
Ab Initio Chemical Kinetic Study for Reactions of H Atoms with SiH(4) and Si(2)H(6): Comparison of Theory and Experiment
(2010-01-14)
Wu, S. Y.
;
Raghunath, P.
;
Wu, J. S.
;
Lin, M. C.
;
機械工程學系
The reactions of hydrogen atom with silane and disilane are relevant to the understanding of catalytic chemical vapor deposition (Cat-CVD) and plasma enhanced chemical vapor deposition (PECVD) processes. In the present study, these reactions have been investigated by means of A initio molecular-orbital and transition-state theory calculations. In both reactions, the most favorable pathway was found to be the H abstraction leading to the formation of SiH(3) and Si(2)H(5) products, with 5.1 and 4.0 kca/mol barriers, respectively. For H + Si(2)H(6), another possible reaction pathway giving SiH(3) + SiH(4) may take place with two different mechanisms with 4.3 and 6.7 kcal/mol barriers for H-atom attacking side-way and end-on, respectively. To validate the calculated energies of the reactions, two isodesmic reactions, SiH(3)+CH(4)-> SiH(4)+CH(3) and Si(2)H(5)+C(2)H(6)-> Si(2)H(6)+C(2)H(5) were employed; the predicted heats of the formation for SiH(3) (49.0 kcal/mol) and Si(2)H(5) (58.6 kcal/mol) were found to agree well with the experimental data. Finally, rate constants for both H-abstraction reactions predicted in the range of 290-2500 K agree well with experimental data. The result also shows that H+Si(2)H(6) producing H(2)+Si(2)H(5) is more favorable than SiH(3)+SiH(4).
Ab Initio Chemical Kinetic Study for Reactions of H Atoms with SiH4 and Si2H6: Comparison of Theory and Experiment
(2010-01-14)
Wu, S. Y.
;
Raghunath, P.
;
Wu, J. S.
;
Lin, M. C.
;
機械工程學系
The reactions of hydrogen atom with silane and disilane are relevant to the understanding of catalytic chemical vapor deposition (Cat-CVD) and plasma enhanced chemical vapor deposition (PECVD) processes. In the present study, these reactions have been investigated by means of A initio molecular-orbital and transition-state theory calculations. In both reactions, the most favorable pathway was found to be the H abstraction leading to the formation of SiH3 and Si2H5 products, with 5.1 and 4.0 kca/mol barriers, respectively. For H + Si2H6, another possible reaction pathway giving SiH3 + SiH4 may take place with two different mechanisms with 4.3 and 6.7 kcal/mol barriers for H-atom attacking side-way and end-on, respectively. To validate the calculated energies of the reactions, two isodesmic reactions, SiH3+CH4 -> SiH4+CH3 and Si2H5+C2H6 -> Si2H6+C2H5 were employed; the predicted heats of the formation for SiH3 (49.0 kcal/mol) and Si2H5 (58.6 kcal/mol) were found to agree well with the experimental data. Finally, rate constants for both H-abstraction reactions predicted in the range of 290-2500 K agree well with experimental data. The result also shows that H+Si2H6 producing H-2+Si2H5 is more favorable than SiH3+SiH4.
Ab Initio Chemical Kinetics for SiH(3) Reactions with Si(x)H(2x+2) (x=1-4)
(2010-12-30)
Raghunath, P.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
Gas-phase kinetics and mechanisms of SiH(3) reactions with SiH(4), Si(2)H(6), Si(3)H(8), and Si(4)H(10), processes of relevance to a-Si thin-film deposition, have been investigated by ab initio molecular orbital and transition-state theory (TST) calculations. Geometric parameters of all the species involved in the title reactions were optimized by density functional theory at the B3LYP and BH&HLYP levels with the 6-311++G(3df,2p) basis set. The potential energy surface of each reaction was refined at the CCSD(T)/6-311++G(3df,2p) level of theory. The results show that the most favorable low energy pathways in the SiH3 reactions with these silanes occur by H abstraction, leading to the formation of SiH(4) + Si(x)H(2x+1)(silanyl) radicals. For both Si(3)H(8) and n-Si(4)H(10) reactions, the lowest energy barrier channels take place by secondary Si-H abstraction, yielding SiH(4) + s-Si(3)H(7) and SiH(4) + s-Si(4)H(9), respectively. In the i-Si(4)H(10) reaction, tertiary Si-H abstraction, has the lowest barrier producing SiH(4) + t-Si(4)H(9). In addition, direct SiH(3)-for-X substitution reactions forming Si(2)H(6) + X (X = H or silanyls) can also occur, but with significantly higher reaction barriers. A comparison of the SiH(3) reactions with the analogous CH(3) reactions with alkanes has been made. The rate constants for low-energy product channels have been calculated for the temperature range 300-2500 K by TST with Eckart tunneling corrections. These results, together with predicted heats of formation of various silanyl radicals and Si(4)H(10) isomers, have been tabulated for modeling of a-Si:H film growth by chemical vapor deposition.
Ab Initio Chemical Kinetics for SiH2 + Si2H6 and SiH3 + Si2H5 Reactions and the Related Uninnolecular Decomposition of Si3H8 under a-Si/H CVD Conditions
(2013-10-24)
Raghunath, P.
;
Lin, M. C.
;
應用化學系
;
Department of Applied Chemistry
The kinetics and mechanisms for SiH2 + Si2H6 and SiH3 + Si2H5 reactions and the related unimolecular decomposition of Si3H8 have been investigated by ab initio molecular orbital theory based on the QCISD(T)/CBS//QCISD/6-311++G(d,p) method in conjunction with quantum statistical variational Rice-Ramsperger-Kassel-Marcus (RR.KM) calculations. For the barrierless radical association processes, their variational transition states have been characterized by the CASPT2//CASSCF method. The species involved in the study are known to coexist under CVD conditions. The results show that the association reaction of SiH2 and Si2H6 producing Si3H8 occurs by insertion via its lowest-energy path forming a loose hydrogen-bonding molecular complex with 8.3 kcal/mol binding energy; the reaction is exothermic by 55.0 kcal/mol. The chemically activated Si3H8 adduct can fragment by several paths, producing SiH4 + SiH3SiH (-0.7 kcal/mol), Si(SiH3)(2) + H-2 (-1.4 kcal/mol), and SiH3SiH2SiH + Hy (-1.4 kcal/mol). The predicted enthalpy changes as given agree well with available thermochemical data. Three other decomposition channels of Si3H8 occurring by Si-H or Si-Si breaking were found to be highly endothermic, and the reactions take place without a well-defined barrier. The heats of formation of Si3H8, SiH2SiH, Si2H4, n-Si3H7, Si(SiH3)(2), and SiH3SiH2SiH have been predicted and found to be in close agreement with those available data in the literature. The product branching rate constants for SiH2 + Si2H6 and SiH3 + Si2H3 reactions and the thermal unimolecular decomposition of Si3H8 for all low-energy paths have been calculated with multichannel variational RRKM theory covering varying P,T conditions typically employed in PECVD and Cat-CVD processes for hydrogenated amorphous silicon (a-Si/H) film growth. The results were also found to be in good agreement with available kinetic data. Our kinetic results may be employed to model and control very large-area a-Si/H film growth for a new generation of solar cell applications.
Ab Initio Chemical Kinetics for SiH3 Reactions with SixH2x+2 (x=1-4)
(2010-12-30)
Raghunath, P.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
Gas-phase kinetics and mechanisms of SiH3 reactions with SiH4, Si2H6, Si3H8, and Si4H10, processes of relevance to a-Si thin-film deposition, have been investigated by ab initio molecular orbital and transition-state theory (TST) calculations. Geometric parameters of all the species involved in the title reactions were optimized by density functional theory at the B3LYP and BH&HLYP levels with the 6-311++G(3df,2p) basis set. The potential energy surface of each reaction was refined at the CCSD(T)/6-311++G(3df,2p) level of theory. The results show that the most favorable low energy pathways in the SiH3 reactions with these silanes occur by H abstraction, leading to the formation of SiH4 + SixH2x+1(silanyl) radicals. For both Si3H8 and n-Si4H10 reactions, the lowest energy barrier channels take place by secondary Si-H abstraction, yielding SiH4 + s-Si3H7 and SiH4 + s-Si4H9, respectively. In the i-Si4H10 reaction, tertiary Si-H abstraction, has the lowest barrier producing SiH4 + t-Si4H9. In addition, direct SiH3-for-X substitution reactions forming Si2H6 + X (X = H or silanyls) can also occur, but with significantly higher reaction barriers. A comparison of the SiH3 reactions with the analogous CH3 reactions with alkanes has been made. The rate constants for low-energy product channels have been calculated for the temperature range 300-2500 K by TST with Eckart tunneling corrections. These results, together with predicted heats of formation of various silanyl radicals and Si4H10 isomers, have been tabulated for modeling of a-Si:H film growth by chemical vapor deposition.
Ab Initio Chemical Kinetics for the CH3 + O(P-3) Reaction and Related Isomerization-Decomposition of CH3O and CH2OH Radicals
(2015-07-16)
Xu, Z. F.
;
Raghunath, P.
;
Lin, M. C.
;
應用化學系
;
Department of Applied Chemistry
The kinetics and mechanism of the CH3 + O reaction and related isomerization-decomposition of CH3O and CH2OH radicals have been studied by ab initio molecular orbital theory based on the CCSD(T)/aug-cc-pVTZ//CCSD/aug-cc-pVTZ, CCSD/aug-cc-pVDZ, and G2M//B3LYP/6-311+G(3df,2p) levels of theory. The predicted potential energy surface of the CH3 + O reaction shows that the CHO + H-2 products can be directly generated from CH3O by the TS3 -> LM1 -> TS7 -> LM2 -> TS4 path, in which both LM1 and LM2 are very loose and TS7 is roaming-like. The result for the CH2O + H reaction shows that there are three low-energy barrier processes including CH2O + H -> CHO + H-2 via H-abstraction and CH2O + H -> CH2OH and CH2O + H -> CH3O by addition reactions. The predicted enthalpies of formation of the CH2OH and CH3O radicals at 0 K are in good agreement with available experimental data. Furthermore, the rate constants for the forward and some key reverse reactions have been predicted at 200-3000 K under various pressures. Based on the new reaction pathway for CH3 + O, the rate constants for the CH2O + H and CHO + H-2 reactions were predicted with the microcanonical variational transition-state/Rice-Ramsperger-Kassel-Marcus (VTST/RRKM) theory. The predicted total and individual product branching ratios (i.e., CO versus CH2O) are in good agreement with experimental data. The rate constant for the hydrogen abstraction reaction of CH2O + H has been calculated by the canonical variational transition-state theory with quantum tunneling and small-curvature corrections to be k(CH2O + H -> CHO + H-2) = 2.28 x 10(-19) T-2.65 exp(-766.5/T) cm(3) molecule(-1) s(-1) for the 200-3000 K temperature range. The rate constants for the addition giving CH3O and CH2OH and the decomposition of the two radicals have been calculated by the microcanonical RRKM theory with the time-dependent master equation solution of the multiple quantum well system in the 200-3000 K temperature range at 1 Torr to 100 atm. The predicted rate constants are in good agreement with most of the available data.
Ab initio chemical kinetics for the ClOO+NO reaction: Effects of temperature and pressure on product branching formation
(1970-01-01)
Raghunath, P.
;
Lin, M. C.
;
應用化學系
;
Department of Applied Chemistry
"The kinetics and mechanism for the reaction of ClOO with NO have been investigated by ab initio molecular orbital theory calculations based on the CCSD(T)/6-311+G(3df)//PW91PW91/6-311+G(3df) method, employed to evaluate the energetics for the construction of potential energy surfaces and prediction of reaction rate constants. The results show that the reaction can produce two key low energy products ClNO + O-3(2) via the direct triplet abstraction path and ClO + NO2 via the association and decomposition mechanism through long-lived singlet pc-ClOONO and ClONO2 intermediates. The yield of ClNO + O-2 ((1)Delta) from any of the singlet intermediates was found to be negligible because of their high barriers and tight transition states. As both key reactions initially occur barrierlessly, their rate constants were evaluated with a canonical variational approach in our transition state theory and Rice-Ramspergen-Kassel-Marcus/master equation calculations. The rate constants for ClNO + O-3(2) and ClO + NO2 production from ClOO + NO can be given by 2.66 x 10(-16) T-1.91 exp(341/T) (200-700 K) and 1.48 x 10(-24) T-3.99 exp(1711/T) (200-600 K), respectively, independent of pressure below atmospheric pressure. The predicted total rate constant and the yields of ClNO and NO2 in the temperature range of 200-700 K at 10-760 Torr pressure are in close agreement with available experimental results. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731883]"
Ab Initio Chemical Kinetics for the HCCO plus H Reaction
(2016)
Pham-Cam Nam
;
Raghunath, P.
;
Huynh, Lam K.
;
Xu, Shucheng
;
Lin, M. C.
Ketenyl radical (HCCO) is an important hydrocarbon combustion intermediate. The mechanisms and kinetics for the reaction of HCCO (X(2)A \'\') with H(S-2) occurring on both singlet and triplet surfaces have been studied by a combination of ab initio calculations and rate constant predictions at the CCSD(T)/6-311++ G(3df,2p)//CCSD/6-311++G(d,p) level of theory. The kinetics and product branching ratios have been investigated in the temperature range of 297-3000 K by variational transition state and Rice-Ramsperger-Kassel-Marcus (RRKM) theories for the production of CH2(a(1)A(1)) + CO(X-1 Sigma(+)) and CH2((XB1)-B-3) + CO(X-1 Sigma(+)). Our prediction for the primary product CH2(a(1)A(1)) + CO(X-1 Sigma(+)) formation is in good agreement with earlier experimental results. The pressure independent rate constant for this channel can be expressed by k(1) (T) = 8.62 x 10(-11)T(0.16)exp(-20/T) cm(3) molecule(-1) s(-1). For the production of CH2((XB1)-B-3) + CO(X-1 Sigma(+)), the rate constant k(2) can be represented as k(2)(T) = 7.63 x 10(-16)T(1.56)exp(-386/T) cm(3) molecule(-1) s(-1). The predicted product branching ratios for the reaction are in close agreement with experimental data as well. We also predicted the heat of formation at 0 K for (HCCO)-H-2, (CCO)-C-3, and (CCO)-C-1 by CCSD(T)/6-311++ G(3df,2p), CBS-QB3, and G2M; the values are in good agreement among one another. Specifically, the CCSD(T) values are:Delta H-f degrees(HCCO, X2A \'\') = 42.52 +/- 0.70; Delta H-f degrees(CCO, (XSg)-S-3) = 91.50 +/- 0.54; and Delta H-f degrees(CCO, a(1)Delta) = 110.22 +/- 0.54 kcal/mol.
Ab initio chemical kinetics for the N2H4 + NOx (x=1-3) reactions and related reverse processes
(2014-10-15)
Raghunath, P.
;
Lin, Y. H.
;
Lin, M. C.
;
交大名義發表
;
應用化學系
The kinetics and mechanisms for N2H4 + NOx, (x = 1-3) reactions and the related reverse reactions have been investigated by ab initio molecular orbital theory based on the CCSD(T)/CBS/ICCSD/6-31G(d,p), CCSD(T)//B3LYP and CCSD(T)//BH&HLYP methods with the 6-311++G(3df,2p) basis set. These reactions are important to the propulsion chemistry of the N2H4-N2O4 propellant system. The results show that the reactions of N2H4 with NO and NO2 producing N2H3 + HNO and N2H3 + c-HONO by H-abstraction with 33.7 and 10.3 kcal/mol barriers, respectively, are dominant. For the N2H4 + NO3(D-3h) reaction via two pre-reaction van der Waals complexes with 0.5 kcal/mol and -1.6 kcal/mol binding energies produces HNO3 + N2H3 by H-abstraction and t-HONO + N2H3O by concerted O- and H-atom transfers, respectively. The predicted enthalpies of formation of various products at 0 K are in good agreement with available experimental data within reported errors. Furthermore, the rate constants for the forward and some key reverse reactions have been predicted in the temperature range 300-2000 K with tunneling corrections using transition state theory (for direct abstraction) and variational Rice-Ramsperger-Kassel-Marcus theory (for association! decomposition) by solving the master equation. (C) 2014 Elsevier B.V. All rights reserved.
Ab Initio Chemical Kinetics for the Reaction of an H Atom with Si(3)H(8)
(2010-03-18)
Varma, D. H.
;
Raghunath, P.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
The kinetics and mechanism for the reaction of H with Si(3)H(8) have been investigated using various theoretical methods including CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311++G(3df,2p), G2M(RCC2), and CCSD(T)/6-311++G(3df,2p)//CCSD/6-311+G(d,p). The results obtained by the latter method show that H abstraction from a primary Si-H bond and a secondary Si-H bond leads to the formation of n-Si(3)H(7) and i-Si(3)H(7) products, with 3.8 (TS1) and 3.2 (TS2) kcal/mol barriers, respectively. Significantly, the hydrogen substitution of SiH(3) and Si(2)H(5) groups by attacking, at the central Si atom via TS3 (3.3 kcal/mol) and a terminal Si atom of Si(3)H(8) from side and end oil (via TS4, 4.2 kcal/mol and TS5, 6.3 kcal/mol), were found to give SiH(3) + Si(2)H(6) and SiH(4) + Si(2)H(5) products, respectively. The heats of formation Of Si(3)H(8), n-Si(3)H(7), and i-Si(3)H(7) at 0 K are predicted to be 32.3 +/- 1.2, 68.6, and 66.6 kcal/mol, respectively. These values are in good agreement with the experimental and other theoretical values. The rate constants and branching ratios for the four product Channels of the title reaction have been calculated by the transition state theory with Eckart tunneling corrections over a wide temperature region of 250-2500 K. These results may be employed for Simulations of catalytic and plasma-enhanced chemical vapor deposition processes of a-Si:H films.
Ab Initio Chemical Kinetics for the Reaction of an H Atom with Si3H8
(2010-03-18)
Varma, D. H.
;
Raghunath, P.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
The kinetics and mechanism for the reaction of H with Si3H8 have been investigated using various theoretical methods including CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311++G(3df,2p), G2M(RCC2), and CCSD(T)/6-311++G(3df,2p)//CCSD/6-311+G(d,p). The results obtained by the latter method show that H abstraction from a primary Si-H bond and a secondary Si-H bond leads to the formation of n-Si3H7 and i-Si3H7 products, with 3.8 (TS1) and 3.2 (TS2) kcal/mol barriers, respectively. Significantly, the hydrogen substitution of SiH3 and Si2H5 groups by attacking, at the central Si atom via TS3 (3.3 kcal/mol) and a terminal Si atom of Si3H8 from side and end oil (via TS4, 4.2 kcal/mol and TS5, 6.3 kcal/mol), were found to give SiH3 + Si2H6 and SiH4 + Si2H5 products, respectively. The heats of formation Of Si3H8, n-Si3H7, and i-Si3H7 at 0 K are predicted to be 32.3 +/- 1.2, 68.6, and 66.6 kcal/mol, respectively. These values are in good agreement with the experimental and other theoretical values. The rate constants and branching ratios for the four product Channels of the title reaction have been calculated by the transition state theory with Eckart tunneling corrections over a wide temperature region of 250-2500 K. These results may be employed for Simulations of catalytic and plasma-enhanced chemical vapor deposition processes of a-Si:H films.
Adsorption Configurations and Decomposition Pathways of Boric Acid on TiO(2) Rutile (110) Surface: A Computational Study
(2009-03-05)
Raghunath, P.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
We have investigated the adsorption and reactions of the monomer and dimer of B(OH)(3) on TiO(2) rutile (110) surface by first-principles calculations. The most stable adsorption structure for B(OH)(3) On the surface is a molecular monodentate configuration, with one hydrogen bonded to a neighboring surface bridging oxygen with an adsorption energy of 20.1 kcal/mol. The adsorbed B(OH)(3) molecule can dissociate into the bidentate adsorption configuration, Ti-OB(OH)O-Ti(a), in which the -OB(OH)O- moiety binds to the surface through two Ti-O bonds with the two dissociated H atoms on neighboring bridged surface oxygen atoms following stepwise H-migration. Notably, the adsorption energy for Ti-OB(OH)O-Ti(a) with 2 H on two O(b) surface atoms is 134.6 kcal/mol. In the case of dimer there are two identical molecules similar to monodentate configuration of B(OH)(3) adsorbed on two 5-fold-coordinated Ti atoms of the surface with an adsorption energy of 37.9 kcal/mol. Following intramolecular dehydration and successive migrations of protons from two OH groups to neighboring Ob sites, very stable Ti-OB(OH)OB(OH)O-Ti adsorbate can be readily formed with 141.1 kcal/mol binding energy. Both Ti-OB(OH)O-Ti(a) and Ti-OB(OH)OB(OH)O-Ti(a) adsorbates can be ideally employed as linkers between semiconductor quantum dots such as metal nitride or selenides and TiO(2) nanoparticles by pretreatment of nanoparticle films with B(OH)(3). A similar study on the adsorption and reactions of B(OH)(3) on anatase (101) surface has been recently reported. The most noticeable difference is that B(OH)(3) and its dimer on the rutile surface have slightly higher binding energies than those on the anatase surface and that the rutile surface is more effective for proton migration from the acid to the surface O-atom.
Adsorption Configurations and Decomposition Pathways of Boric Acid on TiO2 Rutile (110) Surface: A Computational Study
(2009-03-05)
Raghunath, P.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
We have investigated the adsorption and reactions of the monomer and dimer of B(OH)(3) on TiO2 rutile (110) surface by first-principles calculations. The most stable adsorption structure for B(OH)(3) On the surface is a molecular monodentate configuration, with one hydrogen bonded to a neighboring surface bridging oxygen with an adsorption energy of 20.1 kcal/mol. The adsorbed B(OH)(3) molecule can dissociate into the bidentate adsorption configuration, Ti-OB(OH)O-Ti(a), in which the -OB(OH)O- moiety binds to the surface through two Ti-O bonds with the two dissociated H atoms on neighboring bridged surface oxygen atoms following stepwise H-migration. Notably, the adsorption energy for Ti-OB(OH)O-Ti(a) with 2 H on two O-b surface atoms is 134.6 kcal/mol. In the case of dimer there are two identical molecules similar to monodentate configuration of B(OH)(3) adsorbed on two 5-fold-coordinated Ti atoms of the surface with an adsorption energy of 37.9 kcal/mol. Following intramolecular dehydration and successive migrations of protons from two OH groups to neighboring Ob sites, very stable Ti-OB(OH)OB(OH)O-Ti adsorbate can be readily formed with 141.1 kcal/mol binding energy. Both Ti-OB(OH)O-Ti(a) and Ti-OB(OH)OB(OH)O-Ti(a) adsorbates can be ideally employed as linkers between semiconductor quantum dots such as metal nitride or selenides and TiO2 nanoparticles by pretreatment of nanoparticle films with B(OH)(3). A similar study on the adsorption and reactions of B(OH)(3) on anatase (101) surface has been recently reported. The most noticeable difference is that B(OH)(3) and its dimer on the rutile surface have slightly higher binding energies than those on the anatase surface and that the rutile surface is more effective for proton migration from the acid to the surface O-atom.
Adsorption configurations and reactions of boric acid on a TiO(2) anatase (101) surface
(2008-06-05)
Raghunath, P.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
This study investigates the adsorption and reactions of the monomer and dimer of B(OH)(3) on a TiO(2) anatase (101) surface by first-principles calculations based on the density functional theory and pseudopotential method. On the clean surface, the most stable adsorption structure for B(OH)(3) is a molecular monodentate configuration with one hydrogen bonded to a neighboring surface bridging oxygen. The adsorbed B(OH)(3) molecule can dissociate into the bidentate adsorption configuration, Ti-OB(OH)O-Ti(a), in which the -OB(OH)O- moiety binds to the surface through two Ti-O bonds with the two dissociated H atoms on neighboring bridged surface oxygen atoms following two successive H migrations. The overall exothermicity is 10.8 kcal/mol; significantly the adsorption energy for Ti-OB(OH)O-Ti(a) with 2 H's on two O(2c) surface atoms is 140.1 kcal/mol. In the case of the dimer, there are two identical molecules like the monodentate configuration of B(OH)(3) adsorbed on two 5-fold-coordinated Ti atoms of the surface. The Ti-OB(OH)OB(bH)O-Ti binding with 2 H's on two neighboring O(2c) surface atoms is very strong like the monomer case, with 150.0 kcal/mol of adsorption energy. Thus, both Ti-OB(OH)O-Ti and Ti-OB(OH)OB(OH)O-Ti adsorbates can be employed as strong linkers between semiconductor quantum dots such as InN and TiO(2) nanoparticles. The energeties and mechanisms of these surface reactions have also been explicitly predicted with the computed potential energy surfaces. Most of the B(OH)(3) reactions on the anatase surface are exothermic.
Adsorption configurations and reactions of boric acid on a TiO2 anatase (101) surface
(2008-06-05)
Raghunath, P.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
This study investigates the adsorption and reactions of the monomer and dimer of B(OH)(3) on a TiO2 anatase (101) surface by first-principles calculations based on the density functional theory and pseudopotential method. On the clean surface, the most stable adsorption structure for B(OH)(3) is a molecular monodentate configuration with one hydrogen bonded to a neighboring surface bridging oxygen. The adsorbed B(OH)(3) molecule can dissociate into the bidentate adsorption configuration, Ti-OB(OH)O-Ti(a), in which the -OB(OH)O- moiety binds to the surface through two Ti-O bonds with the two dissociated H atoms on neighboring bridged surface oxygen atoms following two successive H migrations. The overall exothermicity is 10.8 kcal/mol; significantly the adsorption energy for Ti-OB(OH)O-Ti(a) with 2 H's on two O-2c surface atoms is 140.1 kcal/mol. In the case of the dimer, there are two identical molecules like the monodentate configuration of B(OH)(3) adsorbed on two 5-fold-coordinated Ti atoms of the surface. The Ti-OB(OH)OB(bH)O-Ti binding with 2 H's on two neighboring O-2c surface atoms is very strong like the monomer case, with 150.0 kcal/mol of adsorption energy. Thus, both Ti-OB(OH)O-Ti and Ti-OB(OH)OB(OH)O-Ti adsorbates can be employed as strong linkers between semiconductor quantum dots such as InN and TiO2 nanoparticles. The energeties and mechanisms of these surface reactions have also been explicitly predicted with the computed potential energy surfaces. Most of the B(OH)(3) reactions on the anatase surface are exothermic.
An Acid-Base Controllable Hierarchical Nanostructure from a NIR-Absorbing Conjugated Polyrotaxane-Based Optical Molecular Switch
(2013-09-10)
Raju, Mandapati V. Ramakrishnam
;
Raghunath, P.
;
Lin, Ming-Chang
;
Lin, Hong-Cheu
;
材料科學與工程學系
To investigate the supramolecular interactions of the mechanically interlocked rotaxane pendants and conjugated polymer backbones, four analogous polymers were systematically synthesized by copolymerization of a 9-alkylidene-9H-fluorene monomer with various monomers, which contained a diketopyrrolopyrrole unit tethered with a dumbbell unit, a metalated [2]rotaxane, a demetalated orthogonal H-bonded [2]rotaxane, and a simple alkyl chain, to furnish P1, P2, P3, and P4, respectively. Prevailing H-1 NMR and UV-vis to NIR titration profiles indicated that the novel polyrotaxane P3 showed a sensitive and reversible acid base molecular switch capability via supramolecular interactions in contrast to the other polymers (P1, P2, and P4). Compared with the other polymers, P3 possessed a narrower bandgap, which was also confirmed by the computational study. Prominently, the monitoring of a controllable nanoself-assembly process of P3 was obtained by reversible acid base molecular switch approaches. The orthogonal H-bonded pendant [2]rotaxane unit and the steric demand of P3 judiciously allowed to morph into a hierarchical nanostructure via interconvertible H-bonds, anion-pi and pi-pi stackings, and hydrophobic interactions.