Photofragmentation of CH3I: Vibrational distribution of the CH3 fragment

Abstract

The photodissociation of CH3I at 266 nm is investigated by means of high resolution photofragment spectroscopy. The resolution is sufficient to determine the vibrational population of the CH3 umbrella motion for the I*(2P1/2)+CH3 product channel. An approximate vibrational distribution for the I(2P3/2)+CH3 product channel is also determined. The rotational energy distribution for the CH3+I*(2P1/2) channel is estimated to be on the order of or less than 600 cm−1 wide for each of the CH3 vibrational states. A refined value for the C–I bond dissociation energy of 53.3±0.7 kcal/mole is determined from the energy threshold for the I*+CH3 channel. The vibrational energy distribution for the I*+CH3 channel is discussed in relation to a recent model calculation by Shapiro and Bersohn and possible explanations for the discrepency between the calculated and the measured distributions are considered.