Desorption Dynamics Of CO From VUV-irradiated Methanol Ice

The translational energies for photodesorbed CO（v=0）from CH₃OH ice have been measured at 157 nm to investigate photodesorption dynamics of CO（v=0）at the temperature of 8,50 and 80 K.The reproduced time-of-flight（TOF）spectrum of CO（v=0）from amorphous CH₃OH ice at 80 K was composed of three different Maxwell-Boltzmann distributions.These components were described by a fast component（A）with T_trans=1250±250K,a middle component（B）with T_trans=450±50K and a slow component（C）with T_trans=90±20 K.The TOF spectra at 8and 50 K were composed of a component（B）and components（A）and（B）,respectively.To reveal the origin of three components,photoproducts on CH₃OH ice were monitored by using Fourier transform reflection absorption infrared spectroscopy（FT-RAIRS）.Based on the TOF spectra and RAIR spectra,it is probable that CO（v=0）was not directly from the photodissociation of CH₃OH,but components（A）and（B）were produced from H₂CO and a component（C）was from CO₂.