Infrared absorption of CH3O and CD3O radicals isolated in solid para-H2

Abstract

Irradiation of a p-H2 matrix containing methyl nitrite (CH3ONO) at 3.2K with laser light at 355nm yielded vibrational fundamental absorption lines at 2773.1/2804.5 (1+ mixed with background states), 2866.5/2887.5?/2967.0? (1− mixed with 4+ and 22−), 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 2E3/2 and 2E1/2, 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)×10−3s−1 after irradiation, likely due to the tunneling reaction of CH3O with p-H2 to form CH2OH.