Electronic absorption spectrum of CH3O

Abstract

The ? 2A1-? 2E electronic transition of CH3O, which is qualitatively analogous to the ? 2Σ+−? 2Πi transition of OH, has been detected in absorption. It consists of a long series of vibronic bands described by ν= (31 538±9)+v′3(676±5)−v′23(5.7±0.6 cm−1), where ν is the transition wavenumber at the band intensity maxima, and v′3 is the upper state C–O stretching vibrational quantum number. The estimated oscillator strength of the transition, f= (4±2) ×10−4, has the same magnitude as in OH. It is shown that the observed C–O vibrational frequencies and vibronic intensities are consistent with the ab initio SCF geometry of CH3O, and with Franck–Condon factors derived from it. Earlier difficulties in detecting the absorption spectrum are attributed to a low absorption coefficient, and to the marginal thermodynamic stability of the CH3O ground state.