Browsing by Author "Bahou, Mohammed"

Now showing 1 - 19 of 19

A new method for investigating infrared spectra of protonated benzene (C6H7+) and cyclohexadienyl radical (c-C6H7) using para-hydrogen
(2012-04-21)
Bahou, Mohammed
;
Wu, Yu-Jong
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
We use protonated benzene (C6H7+) and cyclohexadienyl radical (c-C6H7) to demonstrate a new method that has some advantages over other methods currently used. C6H7+ and c-C6H7 were produced on electron bombardment of a mixture of benzene (C6H6) and para-hydrogen during deposition onto a target at 3.2 K. Infrared (IR) absorption lines of C6H7+ decreased in intensity when the matrix was irradiated at 365 nm or maintained in the dark for an extended period, whereas those of c-C6H7 increased in intensity. Observed vibrational wavenumbers, relative IR intensities, and deuterium isotopic shifts agree with those predicted theoretically. This method, providing a wide spectral coverage with narrow lines and accurate relative IR intensities, can be applied to larger protonated polyaromatic hydrocarbons and their neutral species which are difficult to study with other methods. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3703502]
Absorption cross sections of NH3, NH2D, NHD2, and ND3 in the spectral range 140-220 nm and implications for planetary isotopic fractionation
(2006-08-20)
Cheng, Bing-Ming
;
Lu, Hsiao-Chi
;
Chen, Hong-Kai
;
Bahou, Mohammed
;
Lee, Yuan-Pern
Cross sections for photoabsorption of NH3, NH2D, NHD2, and ND3 in the spectral region 140-220 nm were determined at similar to 298 K using synchrotron radiation. Absorption spectra of NH2D and NHD2 were deduced from spectra of mixtures of NH3 and ND3, of which the equilibrium concentrations for all four isotopologues obey statistical distributions. Cross sections of NH2D, NHD2, and ND3 are new. Oscillator strengths, an integration of absorption cross sections over the spectral lines, for both A X and B X systems of NH3 agree satisfactorily with previous reports; values for NH2D, NHD2, and ND3 agree with quantum chemical predictions. The photolysis of NH3 provides a major source of reactive hydrogen in the lower stratosphere and upper troposphere of giant planets such as Jupiter. Incorporating the measured photoabsorption cross sections of NH3 and NH2D into the Caltech/JPL photochemical diffusive model for the atmosphere of Jupiter, we find that the photolysis efficiency of NH2D is lower than that of NH3 by as much as 30%. The D/H ratio in NH2D/NH3 for tracing the microphysics in the troposphere of Jupiter is also discussed.
Advances in Use of p-H(2) as a Novel Host for Matrix IR Spectroscopy
(2010-08-01)
Bahou, Mohammed
;
Huang, Chiung-Wei
;
Huang, Ya-Ling
;
Glatthaar, Joerg
;
Lee, Yuan-Pern
A review of recent advances in IR spectroscopy using p-H(2) as a matrix host in our laboratory is presented. The softness of this novel p-H, matrix host not only makes high-resolution spectroscopy feasible but also provides new applications. Molecular motion, such as the rotation of C(2)H(4), internal rotation (torsion) of CH(3)OH, and rotation of CH(3)F about a single axis are characterized in this p-H, matrix. In contrast, no evidence for rotation of CH(3)I and CH(3) was found. The diminution of the cage effect leads to the possibility of production of free radicals via either photolysis in situ or bimolecular reactions of molecules with atoms that are produced in situ from their molecular precursors. Taking advantage of these unique features, we identified the IR spectrum of CH(3) produced from photolysis of CH(3)I and CH(3)S produced from photolysis of CH(3)SCH(3) and CH(3)SSCH(3). The reaction of Cl with CS(2) in solid p-H(2) yields ClSCS instead of ClCS(2). The reaction of Cl with HCOOH in solid p-H(2) yields only a complex, Cl center dot HCOOH, not HCl and HOCO. The presence of o-H(2) in trace proportions turned out to be an important factor in the interpretation of IR spectra of species embedded in solid p-H(2). Experimental techniques to minimize the amount of o-H(2) and to characterize its relative concentration with spectra of H(2)O center dot o-H(2) are discussed.
Advances in Use of p-H-2 as a Novel Host for Matrix IR Spectroscopy
(2010-08-01)
Bahou, Mohammed
;
Huang, Chiung-Wei
;
Huang, Ya-Ling
;
Glatthaar, Joerg
;
Lee, Yuan-Pern
A review of recent advances in IR spectroscopy using p-H-2 as a matrix host in our laboratory is presented. The softness of this novel p-H, matrix host not only makes high-resolution spectroscopy feasible but also provides new applications. Molecular motion, such as the rotation of C2H4, internal rotation (torsion) of CH3OH, and rotation of CH3F about a single axis are characterized in this p-H, matrix. In contrast, no evidence for rotation of CH3I and CH3 was found. The diminution of the cage effect leads to the possibility of production of free radicals via either photolysis in situ or bimolecular reactions of molecules with atoms that are produced in situ from their molecular precursors. Taking advantage of these unique features, we identified the IR spectrum of CH3 produced from photolysis of CH3I and CH3S produced from photolysis of CH3SCH3 and CH3SSCH3. The reaction of Cl with CS2 in solid p-H-2 yields ClSCS instead of ClCS2. The reaction of Cl with HCOOH in solid p-H-2 yields only a complex, Cl center dot HCOOH, not HCl and HOCO. The presence of o-H-2 in trace proportions turned out to be an important factor in the interpretation of IR spectra of species embedded in solid p-H-2. Experimental techniques to minimize the amount of o-H-2 and to characterize its relative concentration with spectra of H2O center dot o-H-2 are discussed.
Diminished cage effect in solid p-H(2): Infrared absorption of CH(3)S observed from photolysis in situ of CH(3)SH, CH(3)SCH(3), or CH(3)SSCH(3) isolated in p-H(2) matrices
(2010-10-28)
Bahou, Mohammed
;
Lee, Yuan-Pern
;
應用化學系
;
Department of Applied Chemistry
We report the infrared absorption spectrum of the methylthio (or thiomethoxy) radical, CH(3)S (X(2)E(3/2)), produced via photodissociation in situ of three precursors CH(3)SH, CH(3)SCH(3), and CH(3)SSCH(3) isolated in solid p-H(2). The common absorption features observed with similar intensity ratios in each experiment are assigned to CH(3)S. The wavenumbers of these features agree satisfactorily with those predicted with a spin-vibronic Hamiltonian accounting for the anharmonic effects and the Jahn-Teller effects to the quartic term [A. V. Marenich and J. E. Boggs, J. Chem. Theory Comput. 1, 1162 (2005)]. In addition to an absorption line at 724.2 cm(-1), corresponding to a transition of 3(1) previously determined to be 727 cm(-1) from fluorescence spectra of gaseous CH(3)S, we identified fundamental transitions 6(1)(a(1)) at 771.1, 6(1)(e) at 1056.6, 5(1)(a(1)) at 1400.0, 4(1)(a(1)) at 2898.4 cm(-1), and several combination and overtone transitions. In contrast, photolysis of CH(3)SSCH(3) isolated in solid Ar produces mainly H(2)CS, CH(3)SH, and CS(2), but no CH(3)S. These results demonstrate the feasibility of using photolysis in situ of precursors isolated in solid p-H(2) to produce free radicals by taking advantage of the diminished cage effect of the matrix. (C) 2010 American Institute of Physics. [doi:10.1063/1.3502105]
Diminished cage effect in solid p-H-2: Infrared absorption of CH3S observed from photolysis in situ of CH3SH, CH3SCH3, or CH3SSCH3 isolated in p-H-2 matrices
(2010-10-28)
Bahou, Mohammed
;
Lee, Yuan-Pern
;
應用化學系
;
Department of Applied Chemistry
We report the infrared absorption spectrum of the methylthio (or thiomethoxy) radical, CH3S ((XE3/2)-E-2), produced via photodissociation in situ of three precursors CH3SH, CH3SCH3, and CH3SSCH3 isolated in solid p-H-2. The common absorption features observed with similar intensity ratios in each experiment are assigned to CH3S. The wavenumbers of these features agree satisfactorily with those predicted with a spin-vibronic Hamiltonian accounting for the anharmonic effects and the Jahn-Teller effects to the quartic term [A. V. Marenich and J. E. Boggs, J. Chem. Theory Comput. 1, 1162 (2005)]. In addition to an absorption line at 724.2 cm(-1), corresponding to a transition of 3(1) previously determined to be 727 cm(-1) from fluorescence spectra of gaseous CH3S, we identified fundamental transitions 6(1)(a(1)) at 771.1, 6(1)(e) at 1056.6, 5(1)(a(1)) at 1400.0, 4(1)(a(1)) at 2898.4 cm(-1), and several combination and overtone transitions. In contrast, photolysis of CH3SSCH3 isolated in solid Ar produces mainly H2CS, CH3SH, and CS2, but no CH3S. These results demonstrate the feasibility of using photolysis in situ of precursors isolated in solid p-H-2 to produce free radicals by taking advantage of the diminished cage effect of the matrix. (C) 2010 American Institute of Physics. [doi:10.1063/1.3502105]
Formation and infrared absorption of protonated naphthalenes (1-C10H9+ and 2-C10H9+) and their neutral counterparts in solid para-hydrogen
(2013)
Bahou, Mohammed
;
Wu, Yu-Jong
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
Protonated naphthalene (C10H9+) and its neutral counterparts (hydronaphthyl radicals, C10H9) are important intermediates in the reactions of aromatic compounds and in understanding the unidentified infrared (IR) emissions from interstellar media. We report the IR spectra of 1-C10H9+, 2-C10H9+, 1-C10H9, and 2-C10H9 trapped in solid para-hydrogen (p-H-2); the latter three are new. These species were produced upon electron bombardment of a mixture of naphthalene (C10H8) and p-H-2 during matrix deposition. The intensities of IR features of 1-C10H9+ decreased after the matrix was maintained in darkness for 19 h, whereas those of 1-C10H9 and 2-C10H9 increased. Irradiation of this matrix sample with light at 365 nm diminished lines of 1-C10H9+ and 2-C10H9 and enhanced lines of 1-C10H9 and 2-C10H9+; the latter species was unstable and converted to 1-C10H9+ in less than 30 min and 2-C10H9 was converted to 1-C10H9 at 365 nm. Observed wavenumbers and relative intensities of these species agree satisfactorily with the anharmonic vibrational wavenumbers and IR intensities predicted with the B3PW91/6-311++G(2d,2p) method. Compared with spectra recorded previously with IR photodissociation of Ar-tagged C10H9+ or IR multiphoton dissociation of C10H9+, our method has the advantages of producing high-resolution IR spectra with a wide spectral coverage, true IR intensity and excellent ratio of signal to noise; both protonated species and their neutral counterparts are produced with little interference from other fragments. With these advantages, the IR spectra of 1-C10H9+, 2-C10H9+, 1-C10H9, and 2-C10H9 are here clearly characterized.
Formation and infrared spectra of monohydrogenated pyrenes 2-C16H11 and 4-C16H11 trapped in solid para-hydrogen
(2020-06-05)
Bahou, Mohammed
;
Chou, Sheng-Lung
;
Wu, Yu-Jong
;
應用化學系
;
應用化學系分子科學碩博班
We recorded the IR spectra of 2-C16R11 and 4-C16R11 trapped in solid para-hydrogen (p-H-2). These species were produced on the electron bombardment of p-H-2 containing pyrene (C16H10) in a small proportion during matrix deposition. IR absorption features of 1-C16H11+ and 1-C16H11 in solid p-H-2 were previously identified [J. Phys. Chem. Lett. 4 (2013) 1989]. Here, the irradiation of a similar matrix sample at 365 nm depleted 1-C(16)H(11)(+ )and 2-C16H11 and produced 1-C16H11 and 4-C16H11. In contrast, irradiation at 405 nm decreased 1-C16H11+, 2-C16H11 and 4-C16H11. The identification of the observed lines of 2-C16H11, and 4-C16H11 was supported by predictions of the vibrational wavenumbers and relative IR intensities at the B3PW91/6-311++G(2d,2p) level of theory. (C) 2020 Elsevier B.V. All rights reserved.
Infrared absorption of trans-1-chloromethylallyl and trans-1-methylallyl radicals produced in photochemical reactions of trans-1,3-butadiene and Cl-2 in solid para-hydrogen
(2012-08-28)
Bahou, Mohammed
;
Wu, Jen-Yu
;
Tanaka, Keiichi
;
Lee, Yuan-Pern
;
應用化學系
The reactions of chlorine and hydrogen atoms with trans-1,3-butadiene in solid para-hydrogen (p-H-2) were investigated with infrared (IR) absorption spectra. When a p-H-2 matrix containing Cl-2 and trans-1,3-butadiene was irradiated with ultraviolet light at 365 nm, intense lines at 650.3, 809.0, 962.2, 1240.6 cm(-1), and several weaker ones due to the trans-1-chloromethylallyl radical, center dot(CH2CHCH)CH2Cl, appeared. Observed wavenumbers and relative intensities agree with the anharmonic vibrational wavenumbers and IR intensities predicted with the B3PW91/6-311++g(2d,2p) method. That the Cl atom adds primarily to the terminal carbon atom of trans-1,3-butadiene is in agreement with the path of minimum energy predicted theoretically, but in contrast to the reaction of Cl + propene in solid p-H-2 [J. Amicangelo and Y.-P. Lee, J. Phys. Chem. Lett. 1, 2956 (2010)] in which the addition of Cl to the central C atom is favored, likely through steric effects in a p-H-2 matrix. A second set of lines, intense at 781.6, 957.9, 1433.6, 2968.8, 3023.5, 3107.3 cm(-1), were observed when the UV-irradiated Cl-2/trans-1,3-butadiene/p-H-2 matrix was further irradiated with IR light from a SiC source. These lines are assigned to the trans-1-methylallyl radical, center dot(CH2CHCH)CH3, produced from reaction of 1,3-butadiene with a H atom resulted from the reaction of Cl atoms with solid p-H-2 exposed to IR radiation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4745075]
Infrared identification of the sigma-complex of Cl-C6H6 in the reaction of chlorine atom and benzene in solid para-hydrogen
(2013-02-21)
Bahou, Mohammed
;
Witek, Henryk
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
The reaction of a chlorine atom with benzene (C6H6) is important in organic chemistry, especially in site-selective chlorination reactions, but its product has been a subject of debate for five decades. Previous experimental and theoretical studies provide no concrete conclusion on whether the product is a pi- or sigma-form of the Cl-C6H6 complex. We took advantage of the diminished cage effect of para-hydrogen (p-H-2) to produce Cl in situ to react with C6H6 (or C6D6) upon photolysis of a Cl-2/C6H6 (or C6D6)/p-H-2 matrix at 3.2 K. The infrared spectrum, showing intense lines at 1430.5, 833.6, 719.8, 617.0, and 577.4 cm(-1), and several weaker ones for Cl-C6H6, and the deuterium shifts of observed new lines unambiguously indicate that the product is a 6-chlorocyclohexadienyl radical, i.e., the sigma-complex of Cl-C6H6. Observation of the s-complex rather than the pi-complex indicates that the s-complex is more stable in solid p-H-2 at 3.2 K. The spectral information is crucial for further investigations of the Cl + C6H6 reaction either in the gaseous or solution phase. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4790860]
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 ovalene (C32H14) and hydrogenated ovalene (C32H15 center dot) in solid para-hydrogen
(2016-11-07)
Tsuge, Masashi
;
Bahou, Mohammed
;
Wu, Yu-Jong
;
Allamandola, Louis
;
Lee, Yuan-Pern
We report the infrared (IR) spectra of ovalene (C32H14) and hydrogenated ovalene (C32H15 center dot) in solid para-hydrogen (p-H-2). The hydrogenated ovalene and protonated ovalene were generated from electron bombardment of a mixture of ovalene and p-H-2 during deposition of a matrix at 3.2 K. The features that decreased with time have been previously assigned to 7-C32H15+, the most stable isomer of protonated ovalene (Astrophys. J., 2016, 825, 96). The spectral features that increased with time are assigned to the most stable isomer of hydrogenated ovalene (7-C32H15 center dot) based on the expected chemistry and on a comparison with the vibrational wavenumbers and IR intensities predicted by the B3PW91/6-311++ G(2d, 2p) method. The mechanism of formation of 7-C32H15 center dot is discussed according to the observed changes in intensity and calculated energetics of possible reactions of H + C32H14 and isomerization of C32H15 center dot. The formation of 7-C32H15 center dot is dominated by the reaction H + C32H14 -> 7-C32H15 center dot, implying that, regardless of the presence of a barrier, the hydrogenation of polycyclic aromatic hydrocarbons occurs even at 3.2 K.
Infrared spectra of protonated coronene and its neutral counterpart in solid parahydrogen: Implications for the unidentified interstellar infrared emission bands
(2014-03-16)
Bahou, Mohammed
;
Wu, Yu-Jung
;
Lee, Yuan-Pern
;
應用化學系
;
Department of Applied Chemistry
Infrared Spectra of Protonated Coronene and Its Neutral Counterpart in Solid Parahydrogen: Implications for Unidentified Interstellar Infrared Emission Bands
(2014-01-20)
Bahou, Mohammed
;
Wu, Yu-Jong
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
Large protonated polycyclic aromatic hydrocarbons (H(+)PAHs) are possible carriers of unidentified infrared (UIR) emission bands from interstellar objects, but the characterization of infrared (IR) spectra of large H(+)PAHs in the laboratory is challenging. IR absorption spectra of protonated coronene (1-C24H13+) and mono-hydrogenated coronene (1-C24H13.), which were produced upon electron bombardment of parahydrogen containing a small proportion of coronene (C24H12) during matrix deposition, were recorded. The spectra are of a much higher resolution than those obtained by IR multiphoton dissociation by Dopfer and co-workers. The IR spectra of protonated pyrene and coronene collectively appear to have the required chromophores for features of the UIR bands, and the spectral shifts on an increase in the number of benzenoid rings point in the correct direction towards the positions of the UIR bands. Larger protonated peri-condensed PAHs might thus be key species among the carriers of UIR bands.
Infrared Spectra of Protonated Pyrene and Its Neutral Counterpart in Solid para-Hydrogen
(2013-06-20)
Bahou, Mohammed
;
Wu, Yu-Jong
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
Protonated polycyclic aromatic hydrocarbons (H(+)PAHs) have been reported to have infrared (IR) bands at wavenumbers near those of unidentified infrared (UIR) emission bands from interstellar objects. We produced 1-C16H11+ and 1-C16H11 upon electron bombardment during matrix deposition of p-H-2 containing pyrene (C16H10) in a small proportion. Intensities of absorption features of 1-C16H11+ decreased after the matrix was maintained in darkness or irradiated with light at 365 nm, whereas those of 1-C16H11 increased. The observed line wavenumbers and relative intensities of 1-C16H11+ and 1-C16H11 agree satisfactorily with the scaled vibrational wavenumbers and IR intensities predicted with the B3PW91/6-311++G(2d,2p) method. Our method, being relatively clean with negligible fragmentation, is applicable to larger H(+)PAH; it has the advantages of producing excellent IR spectra covering a broad spectral range with narrow lines and accurate intensities, so that structural identification among various isomers is feasible.
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.
Infrared spectrum of the 2-chloroethyl radical in solid para-hydrogen
(2012)
Amicangelo, Jay C.
;
Golec, Barbara
;
Bahou, Mohammed
;
Lee, Yuan-Pern
;
應用化學系
The addition reaction of chlorine with ethylene (C(2)H(4)) is expected to proceed via a free radical intermediate, the 2-chloroethyl radical, however, this intermediate has not been previously observed spectroscopically. Irradiation at 365 nm of a co-deposited mixture of Cl(2), C(2)H(4), and p-H(2) at 3.2 K produces a series of new lines in the infrared spectrum. A strong line at 664.0 cm(-1) and weaker lines at 562.1, 1069.9, 1228.0, 3041.1 and 3129.3 cm(-1) are concluded to be due to a single carrier based on their behavior upon subsequent annealing to 4.5 K and secondary irradiation at 254 and 214 nm. The positions and intensities of these lines agree with the MP2/aug-cc-pVDZ predicted vibrational spectrum of the 2-chloroethyl ((center dot)CH(2)CH(2)Cl) radical. In order to confirm this assignment, isotopic experiments were performed with C(2)D(4) and t-C(2)H(2)D(2) and the corresponding infrared bands due to the deuterium isotopomers of this radical ((center dot)CD(2)CD(2)Cl and (center dot)C(2)H(2)D(2)Cl) have been observed. A final set of experiments were performed following irradiation of the Cl(2)/C(2)H(4)/p-H(2) mixture at 365 nm, in which the matrix was irradiated with filtered infrared light from a globar source, which has been shown to induce reactions between isolated Cl atoms and matrix H(2) to produce HCl and H atoms. In these experiments, the major products observed were HCl, the ethyl radical (center dot C(2)H(5)) and ethyl chloride (C(2)H(5)Cl) and the possible mechanisms for the formation of these species are discussed.
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]
THE INFRARED SPECTRUM OF PROTONATED OVALENE IN SOLID PARA-HYDROGEN AND ITS POSSIBLE CONTRIBUTION TO INTERSTELLAR UNIDENTIFIED INFRARED EMISSION
(2016-07-10)
Tsuge, Masashi
;
Bahou, Mohammed
;
Wu, Yu-Jong
;
Allamandola, Louis
;
Lee, Yuan-Pern
The mid-infrared emission from galactic objects, including reflection nebulae, planetary nebulae, proto-planetary nebulae, molecular clouds, etc, as well as external galaxies, is dominated by the unidentified infrared (UIR) emission bands. Large protonated polycyclic aromatic hydrocarbons (H(+)PAHs) were proposed as possible carriers, but no spectrum of an H(+)PAH has been shown to exactly match the UIR bands. Here, we report the IR spectrum of protonated ovalene (7-C32H15+) measured in a para-hydrogen (p-H-2) matrix at 3.2 K, generated by bombarding a mixture of ovalene and p-H-2 with electrons during matrix deposition. Spectral assignments were made based on the expected chemistry and on the spectra simulated with the wavenumbers and infrared intensities predicted with the B3PW91/6-311++G(2d, 2p) method. The close resemblance of the observed spectral pattern to that of the UIR bands suggests that protonated ovalene may contribute to the UIR emission, particularly from objects that emit Class A spectra, such as the IRIS reflection nebula, NGC 7023.