Photodissociation of acetaldehyde as a second example of the roaming mechanism

Product state distributions of the CO produced in the 308-nm photolysis of acetalclehyde show clear evidence of two dissociation mechanisms. One is attributed to the conventional transition state mechanism predicted by theory, with high rotational and translational energy of the CO and a pronounced v perpendicular to J vector correlation. However, as much as 15% of the reaction flux proceeds via another pathway that produces low CO rotational and translational energy, very high CH4 internal energy, and no correlation between the CO velocity and angular momentum vectors. The attributes of this channel are dynamically similar to the recently reported roaming atom mechanism in formaldehyde. We therefore speculate that the second pathway in acetalclehyde also occurs via a roaming mechanism in the CH3 + HCO exit channel that decays into the CH4 + CO channel.