Browsing by Author "Sibert, Edwin L., III"

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Infrared absorption of CH3O and CD3O radicals isolated in solid para-H-2
(2015-04-01)
Lee, Yu-Fang
;
Chou, Wei-Te
;
Johnson, Britta A.
;
Tabor, Daniel P.
;
Sibert, Edwin L., III
Irradiation of a p-H-2 matrix containing methyl nitrite (CH3ONO) at 3.2 K with laser light at 355 nm yielded vibrational fundamental absorption lines at 2773.1/2804.5 (1(+) mixed with background states), 2866.5/2887.5?/2967.07 (1(-) mixed with 4(+) and 2(2)(-)), 1365.7 (2(+)), 1411.3 (2(-)), 1041.8 (3), 2901.3?/ 2917.4/2982.2 (4(-) mixed with background states), 2940.5 (4(+)), 1346.8 (5(+)), 1427.2 (5(-)), 1519.9 (5(+)), 1523.0 (5(-)), 689.3/694.4 (6(+)), 945.9/951.7 (6(-)), 1224.6/1228.9 (6(+)), and 1233.7/1239.1 (6(-)) cm(-1) that are assigned to the methoxy (CH3O) radical; the numbers in parentheses indicate vibrational normal modes, the superscript + and - indicate the spin-orbit components E-2(3/2) and E-2(1/2), respectively, and the "?" marks indicate tentative assignments. Experiments with CD3ONO yielded lines of CD3O at 2012.4? (1(-)), 1005.9 (3(+)), 1037.3 (3(-)), 2168.8 (4(+)), 2174.9 (4(+)), 2202.8 (4(-)), 2212.3 (4(-)), 974.3 (5(+)), 1185.2 (5(+)), 1224.8 (5(-)), 529.6/531.3 (6(+)), 728.3/731.3 (6(-)), 912.4 (6(+)), and 923.2 (6(-)) cm(-1). Many additional lines associated with combination or overtone modes were also observed. The assignments are based on the photolytic behavior and comparisons of observed vibrational wavenumbers and IR intensities with those predicted with a fitted CCSD(T)/cc-pVTZ force field; deviations between experiments and fitted theoretical results are within 2% with an average value (0.4 +/- 0.4)%. These newly observed spectra show vibrational wavenumbers of CH3O consistent with most vibrational energies derived from stimulated-emission-pumping experiments on gaseous CH3O and those of CD3O are consistent with some lines derived from laser-induced fluorescence. Intensities of these lines of CH3O diminished with a rate coefficient (7.6 +/- 0.3) x 10(-3) s(-1) after irradiation, likely due to the tunneling reaction of CH3O with p-H-2 to form CH2OH. (C) 2014 Elsevier Inc. All rights reserved.
Infrared absorption spectra of partially deuterated methoxy radicals CH2DO and CHD2O isolated in solid para-hydrogen
(2017-10-21)
Haupa, Karolina A.
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Johnson, Britta A.
;
Sibert, Edwin L., III
;
Lee, Yuan-Pern
;
應用化學系
The investigation of partially deuterated methoxy radicals is important because the symmetry lowering from C-3v to C-s provides new insights into the couplings between rovibronic states via Jahn-Teller and spin-orbit interactions. The vibrational spectrum of the partially deuterated methoxy radical CH2DO in a matrix of p-H-2 has been recorded. This species was prepared by irradiating a p-H-2 matrix containing deuterated d1-nitritomethane (CH2DONO) at 3.3 K with laser light at 355 nm. The identification of the radical is based on the photochemical behavior of the precursor and comparison of observed vibrational wavenumbers and infrared (IR) intensities with those predicted from a refined quartic, curvilinear, internal coordinate force field calculated with the coupled-cluster singles and doubles with perturbative triples/cc-pVTZ method. CH2DO reacts with H-2 with a rate coefficient (3.5 +/- 1.0) x 10(-3) s(-1). Predominantly c-CHDOH and a negligibly small amount of t-CHDOH were produced. This stereoselectivity results from the reaction H + C-s-CH2DOH, which was demonstrated by an additional experiment on irradiation of a CH2DOH/Cl-2/p-H-2 matrix with ultraviolet and IR light to induce the H + CH2DOH reaction; only c-CHDOH was observed from this experiment. Even though the energies of transition states and products for the formation of c-CHDOH and t-CHDOH differ by only similar to 10 cm(-1), the selective formation of c-CHDOH can be explained by tunneling of the hydrogen atom via an optimal tunneling path. Similarly, the vibronic spectrum for the partially deuterated specie d(2)-methoxy radical (CHD2O) was obtained upon irradiation of d(2)-nitritomethane (CHD2ONO) at 355 nm. Lines associated with the fundamental vibrational modes were observed and assigned; line positions agree with theoretically predicted vibrational wavenumbers. CHD2O reacts with H-2 with a rate coefficient (6.0 +/- 1.4) x 10(-3) s(-1); CD2OH was produced as a major product because the barrier for the formation of CHDOH from H + CHD2OH is greater by similar to 400 cm(-1). Rate coefficients of the decays of CH3O, CH2DO, CHD2O, and CD3O and their corresponding potential energy surfaces are compared. Published by AIP Publishing.