Action Spectroscopy and Photodissociation of Vibrationally Excited Methanol

Abstract

Vibrationally mediated photodissociation combined with time-of-flight detection of product H-atoms provides an electronic excitation action spectrum of jet-cooled methanol containing one quantum of O−H stretching excitation. The maximum in the electronic excitation spectrum of vibrationally excited methanol is about 2600 cm-1 lower in total excitation energy than that for ground vibrational state methanol. A simple model using a one-dimensional vibrational wave function mapped onto a dissociative excited electronic state surface recovers the qualitative features of the spectrum. Using ab initio calculations of portions of the ground and excited potential energy surfaces, we calculate vibrational wave functions and simulate the electronic excitation spectra using the overlap integral for the bound and dissociative vibrational wave functions on the two surfaces. The qualitative agreement of the calculation with the measurement suggests that at the energy of the fundamental vibration the O−H stretch is largely uncoupled from the rest of the molecule during the dissociation.