Excited-state dynamics of CHI and CHIBr studied with UV-pump VUV-probe momentum-resolved photoion spectroscopy.

We perform time-resolved ionization spectroscopy measurements of the excited state dynamics of CHI and CHIBr following photoexcitation in the deep UV. The fragment ions produced by ionization with a vacuum-ultraviolet probe pulse are measured with velocity map imaging, and the momentum resolved yields are compared with trajectory surface hopping calculations of the measurement observable. Together with recent time-resolved photoelectron spectroscopy measurements of the same dynamics, these results provide a detailed picture of the coupled electronic and nuclear dynamics involved. Our measurements highlight the non-adiabatic coupling between electronic states, which leads to notable differences in the dissociation dynamics for the two molecules.