State-specific unimolecular dissociation dynamics of HFCO. II. CO rotational distribution and Doppler widths

Abstract

Rovibrational state distributions and Doppler widths of CO fragments formed from unimolecular dissociation of HFCO in its ground electronic state are measured by vacuum ultraviolet laser-induced fluorescence, following state-selective preparation of the molecule in a single quantum state in the energy region of 2000 to 3000 cm−1 above the dissociation threshold by stimulated emission pumping. CO fragments are rotationally hot and distributed over J≤15 to J=63 with distributions peaking at J=45 to 50 depending upon the initial HFCO dissociative state. Although CO rotational distributions are significantly different for different initial states, about 20% of the total available energy is released on average as rotational energy of CO for all three initial states studied. The yield of CO(v=1) fragments is determined to be about 10% and CO(v≥2) fragments are not observed. The average Doppler width of CO fragments is 0.85 cm−1, which indicates that ∼50% of the total available energy is released as translation. The CO product state distributions and Doppler widths may be rationalized using a modified impulsive model with the ab initio transition state geometry. The dependence of product state distributions on the initial HFCO quantum state may reflect incomplete intramolecular vibrational energy redistribution.