Photofragment infrared emission spectroscopy: Vibrational progression and potential parameters of the CH3(ν2) ‘‘umbrella’’ mode

Abstract

The out‐of‐plane bending vibration (ν₂) of the free radical CH₃ has been detected by time and wavelength‐resolved infrared emission spectroscopy following dissociation of CH₃I with a pulsed laser at λ = 266 nm. Three distinct Q branch features in the vibrational progression of the ν₂ ’’umbrella’’ mode are observed: 3‐2 (729±4 cm⁻¹), 4‐3 (772±4 cm⁻¹), and 5‐4 (811±4 cm⁻¹). These low resolution measurements provide an approximate determination of the harmonic/quartic mixed oscillator potential parameters for the higher levels of the out‐of‐plane bend. The vibrational assignment is important to studies of radical excitation originating from photodissociation, which is considered in the accompanying paper.