INFRARED ABSORPTION OF CH3O/CD3O RADICALS PRODUCED UPON PHOTOLYSIS OF CH3ONO/CD3ONO IN A p-H2 MATRIX

The methoxy radical, CH3O, has attracted much attention because of its important molecular structure and also as a reaction intermediate in combustion and atmospheric chemistry. Previous investigations include laser-induced fluorescence, laser magnetic resonance, and stimulated emission pumping. High-resolution infrared spectrum of jet-cooled CH3O, produced by laser photolysis of CH3ONO, in the C-H stretching region 2850-2940 cm−1 has been reported.a However, direct infrared absorption spectrum of CH3O other than the C–H stretching region remains unreported. Irradiation of a p-H2 matrix containing CH3ONO at 3.2 K with UV light produced main features at 1365.4, 1427.5 (21, 21), 1041.8 (31), 1346.8, 1427.5, 1520.9, 1520.9 (51, 51, 51, 51), and 689.3/694.9, 945.9/951.7, 1233.5, 1235.9 cm−1 (61, 61, 61, 61); labels 2-6 in parentheses indicate transitions to vibrational states attributable to the umbrella, C–O stretching, CH2 scissoring, and HCO deformation modes of CH3O, respectively. These features appeared upon photolysis and diminished after five minutes; formation of CH2OH was observed as CH3O decayed. The assignments were based on comparison of observed vibrational wavenumbers with those predicted with the quadratic potential energy force field and quadratic dipole moment expansion calculated with the CCSD(T)/cc-pVTZ method.b Jahn-Teller and anharmonic vibrational contributions were included in the full Hamiltonian to estimate the correlation diagram connecting the harmonic eigenvalues to those of the fully coupled problem. Similarly, lines of CD3O were observed upon UV photolysis of CD3ONO, but became diminished within five minutes. These observations demonstrates the advantage of diminished cage effect of solid p-H2; CH3O and CD3O are produced via insitu UV photodissociation of CH3ONO isolated in p-H2, but not in Ar or Ne.