Browsing by Author "Das, Prasanta"

Now showing 1 - 7 of 7

Bimolecular reaction of CH3 + CO in solid p-H-2: Infrared absorption of acetyl radical (CH3CO) and CH3-CO complex
(2014-06-28)
Das, Prasanta
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
We have recorded infrared spectra of acetyl radical (CH3CO) and CH3-CO complex in solid para-hydrogen (p-H-2). Upon irradiation at 248 nm of CH3C(O)Cl/p-H-2 matrices, CH3CO was identified as the major product; characteristic intense IR absorption features at 2990.3 (v(9)), 2989.1 (v(1)), 2915.6 (v(2)), 1880.5 (v(3)), 1419.9 (v(10)), 1323.2 (v(5)), 836.6 (v(7)), and 468.1 (v(8)) cm (1) were observed. When CD3C(O)Cl was used, lines of CD3CO at 2246.2 (v(9)), 2244.0 (v(1)), 1866.1 (v(3)), 1046.7 (v(5)), 1029.7 (v(4)), 1027.5 (v(10)), 889.1 (v(6)), and 723.8 (v(7)) cm (1) appeared. Previous studies characterized only three vibrational modes of CH3CO and one mode of CD3CO in solid Ar. In contrast, upon photolysis of a CH3I/CO/p-H-2 matrix with light at 248 nm and subsequent annealing at 5.1 K before re-cooling to 3.2 K, the CH3-CO complex was observed with characteristic IR features at 3165.7, 3164.5, 2150.1, 1397.6, 1396.4, and 613.0 cm(-1). The assignments are based on photolytic behavior, observed deuterium isotopic shifts, and a comparison of observed vibrational wavenumbers and relative IR intensities with those predicted with quantum-chemical calculations. This work clearly indicates that CH3CO can be readily produced from photolysis of CH3C(O)Cl because of the diminished cage effect in solid p-H-2 but not from the reaction of CH3 + CO because of the reaction barrier. Even though CH3 has nascent kinetic energy greater than 87 kJ mol(-1) and internal energy similar to 42 kJ mol(-1) upon photodissociation of CH3I at 248 nm, its energy was rapidly quenched so that it was unable to overcome the barrier height of similar to 27 kJ mol(-1) for the formation of CH3CO from the CH3 + CO reaction; a barrierless channel for formation of a CH3-CO complex was observed instead. This rapid quenching poses a limitation in production of free radicals via bimolecular reactions in p-H-2. (C) 2014 AIP Publishing LLC.
Bimolecular reaction of CH3 + CO in solid p-H-2: Infrared absorption of acetyl radical (CH3CO) and CH3-CO complex
(2014-06-28)
Das, Prasanta
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
We have recorded infrared spectra of acetyl radical (CH3CO) and CH3-CO complex in solid para-hydrogen (p-H-2). Upon irradiation at 248 nm of CH3C(O)Cl/p-H-2 matrices, CH3CO was identified as the major product; characteristic intense IR absorption features at 2990.3 (v(9)), 2989.1 (v(1)), 2915.6 (v(2)), 1880.5 (v(3)), 1419.9 (v(10)), 1323.2 (v(5)), 836.6 (v(7)), and 468.1 (v(8)) cm (1) were observed. When CD3C(O)Cl was used, lines of CD3CO at 2246.2 (v(9)), 2244.0 (v(1)), 1866.1 (v(3)), 1046.7 (v(5)), 1029.7 (v(4)), 1027.5 (v(10)), 889.1 (v(6)), and 723.8 (v(7)) cm (1) appeared. Previous studies characterized only three vibrational modes of CH3CO and one mode of CD3CO in solid Ar. In contrast, upon photolysis of a CH3I/CO/p-H-2 matrix with light at 248 nm and subsequent annealing at 5.1 K before re-cooling to 3.2 K, the CH3-CO complex was observed with characteristic IR features at 3165.7, 3164.5, 2150.1, 1397.6, 1396.4, and 613.0 cm(-1). The assignments are based on photolytic behavior, observed deuterium isotopic shifts, and a comparison of observed vibrational wavenumbers and relative IR intensities with those predicted with quantum-chemical calculations. This work clearly indicates that CH3CO can be readily produced from photolysis of CH3C(O)Cl because of the diminished cage effect in solid p-H-2 but not from the reaction of CH3 + CO because of the reaction barrier. Even though CH3 has nascent kinetic energy greater than 87 kJ mol(-1) and internal energy similar to 42 kJ mol(-1) upon photodissociation of CH3I at 248 nm, its energy was rapidly quenched so that it was unable to overcome the barrier height of similar to 27 kJ mol(-1) for the formation of CH3CO from the CH3 + CO reaction; a barrierless channel for formation of a CH3-CO complex was observed instead. This rapid quenching poses a limitation in production of free radicals via bimolecular reactions in p-H-2. (C) 2014 AIP Publishing LLC.
Infrared absorption of 3-propenonyl (center dot CH2CHCO) radical generated upon photolysis of acryloyl chloride [CH2CHC(O)Cl] in solid para-H-2
(2013-08-28)
Das, Prasanta
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
Irradiation at 193 nm of a p-H-2 matrix containing acryloyl chloride CH2CHC(O)Cl at 3.2 K yielded infrared absorption lines at 3143.6 (nu(1)), 3057.0 (nu(2)), 3048.0 (nu(3)), 2103.1 (nu(4)), 1461.0 (nu(5)), 1349.8 (nu(6)), 1223.7 (nu(11)+nu(12) or 2 nu(12)), 1092.8 (nu(8)), 918.1 (nu(9)), 691.0 (nu(10)), 624.3 (nu(11)), and 597.1 (nu(12)) cm (1) that are assigned to the 3-propenonyl (center dot CH2CHCO) radical. The assignments are based on the photolytic behavior and a comparison of observed vibrational wavenumbers and infrared intensities with those predicted with the B3PW91/aug-cc-pVDZ method. The observation is consistent with a major radical formation channel CH2CHCO + Cl followed by escape of the Cl atom from the original p-H-2 cage. The observation of 3-propenonyl (center dot CH2CHCO) radical but not 3-propenalyl (s-cis- or s-trans-CH2CH(C) over dotO) radical indicates that the former is the most stable isomer and that the barrier heights for conversion from s-cis- or s-trans-CH2CH(C) over dotO to center dot CH2CHCO are small. (C) 2013 AIP Publishing LLC.
Infrared absorption of t-HOCO+, H+(CO2)(2), and HCO2- produced in electron bombardment of CO2 in solid para-H-2
(2016-07-07)
Das, Prasanta
;
Tsuge, Masashi
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
We have employed electron bombardment during matrix deposition of CO2 (or (CO2)-C-13, (CO2)-O-18) and para-hydrogen (p-H-2) at 3.2 K and recorded infrared (IR) spectra of t-HOCO+, H+(CO2)(2) , HCO2-, CO2-, t-HOCO, and other species isolated in solid p-H-2. After the matrix was maintained in darkness for 13 h, intensities of absorption features of t-HOCO+ at 2403.5 (v(1)), 2369.9 (v(2)), 1018.1 (v(4)), and 606.5 (v(6)) cm(-1) and those of H+(CO2)(2) at 1341.1, 883.6, and 591.5 cm(-1) decreased. Corresponding lines of isotopologues were observed when (CO2)-C-13 or (CO2)-O-18 replaced CO2. In contrast, lines of HCO2- at 2522.4 (v(1)), 1616.1 (v(5)), 1327.9 (v(2)), and 745.6 (v(3)) cm(-1) increased in intensity; corresponding lines of (HCO2-)-C-13 or (HCO2-)-O-18 were also observed. Lines of t-DOCO+ and DCO2- were observed in an electron bombarded CO2/normal-deuterium (n-D-2) matrix. Data of v(6) of t-HOCO+ and all observed modes of (HOCO+)-O-18-O-18 and (HCO2-)-O-18 are new. The assignments were made according to expected chemical behavior, observed isotopic shifts, and comparisons with vibrational wavenumbers and relative intensities of previous reports and calculations with the B3PW91/aug-cc-pVQZ method. The v(1) line of t-HOCO+ in solid p-H-2 (2403.5 cm(-1)), similar to the line at 2673 cm(-1) of t-HOCO+ tagged with an Ar atom, is significantly red-shifted from that reported for gaseous t-HOCO+ (3375.37 cm(-1)) due to partial proton sharing between CO2 and H-2 or Ar. The v(1) line of HCO2- in solid p-H-2 (2522.4 cm(-1)) is blue shifted from that reported for HCO2- in solid Ne (2455.7 cm(-1)) and that of HCO2- tagged with Ar (2449 cm(-1)); this can be explained by the varied solvation effects by Ne, Ar, or H-2 on the mixing of H+ + CO2 and H+ CO2- surfaces. Possible formation mechanisms of t-HOCO+, H+(CO2)(2), HCO2-, CO2-, t-HOCO, H2O, and t-HCOOH are discussed. Published by AIP Publishing.
Infrared spectra of free radicals and protonated species produced in para-hydrogen matrices
(2014)
Bahou, Mohammed
;
Das, Prasanta
;
Lee, Yu-Fang
;
Wu, Yu-Jong
;
Lee, Yuan-Pern
The quantum solid para-hydrogen (p-H-2) has emerged as a new host for matrix isolation experiments. Among several unique characteristics, the diminished cage effect enables the possibility of producing free radicals via either photolysis in situ or bimolecular reactions of molecules with atoms or free radicals that are produced in situ from their precursors upon photo-irradiation. Many free radicals that are unlikely to be produced in noble-gas matrices can be produced readily in solid p-H-2. In addition, protonated species can be produced upon electron bombardment of p-H-2 containing a small proportion of the precursor during deposition. The application of this novel technique to generate protonated polycyclic aromatic hydrocarbons (PAH) and their neutral counterparts demonstrates its superiority over other methods. The technique of using p-H-2 as a matrix host has opened up many possibilities for the preparation of free radicals and unstable species and their spectral characterization. Many new areas of applications and fundamental understanding concerning the p-H-2 matrix await further exploration.
Infrared Spectra of the 1-Pyridinium (C5H5NH+) Cation and Pyridinyl (C5H5NH and 4-C5H6N) Radicals Isolated in Solid para-Hydrogen
(2013-12-19)
Golec, Barbara
;
Das, Prasanta
;
Bahou, Mohammed
;
Lee, Yuan-Pern
;
應用化學系
Protonated pyridine and its neutral counterparts (C5H6N) are important intermediates in organic and biological reactions and in the atmosphere. We have recorded the IR absorption spectra of the 1-pyriclinium (C5H5-NH+) cation, 1-pyridinyl (C5H5NH), and 4-pyridinyl (4-C5H6N) produced on electron bombardment during matrix deposition of a mixture of pyridine (C5H5N) and p-H-2 at 3.2 K; all spectra were previously unreported. The IR features of C5H5NH+ diminished in intensity after the matrix was maintained in darkness for 15 h, whereas those of C5H5NH and 4-C5H6N radicals increased. Irradiation of this matrix with light at 365 nm diminished lines of C5H5NH+ and C but enhanced lines of 4-C5H6N slightly, whereas irradiation at 405 nm diminished lines of 4-C5H6N significantly. Observed wavenumbers and relative intensities of these species agree satisfactorily with the anharmonic vibrational wavenumbers and IR intensities predicted with the B3LYP/6-31++G(d,p) method. Assignments of C5H5NH and 4-C5H6N radicals were further supported by the observation of similar spectra when a CI2/C5H5N5N/p-H-2 matrix was irradiated first at 365 nm and then with IR light to generate H atoms to induce the H + C5H5N reaction.
Reactions between atomic chlorine and pyridine in solid para-hydrogen: Infrared spectrum of the 1-chloropyridinyl (C5H5N-Cl) radical
(2013-02-07)
Das, Prasanta
;
Bahou, Mohammed
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
With infrared absorption spectra we investigated the reaction between Cl atom and pyridine (C5H5N) in a para-hydrogen (p-H-2) matrix. Pyridine and Cl-2 were co-deposited with p-H-2 at 3.2 K; a planar C5H5N-Cl-2 complex was identified from the observed infrared spectrum of the Cl-2/C5H5N/p-H-2 matrix. Upon irradiation at 365 nm to generate Cl atom in situ and annealing at 5.1 K for 3 min to induce secondary reaction, the 1-chloropyridinyl radical (C5H5N-Cl) was identified as the major product of the reaction Cl + C5H5N in solid p-H-2; absorption lines at 3075.9, 1449.7, 1200.6, 1148.8, 1069.3, 1017.4, 742.9, and 688.7 cm(-1) were observed. The assignments are based on comparison of observed vibrational wavenumbers and relative IR intensities with those predicted using the B3PW91/6-311++G(2d, 2p) method. The observation of the preferential addition of Cl to the N-site of pyridine to form C5H5N-Cl radical but not 2-, 3-, or 4-chloropyridine (ClC5H5N) radicals is consistent with the reported theoretical prediction that formation of the former proceeds via a barrierless path. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789407]