Photolysis of methyl nitrate (CH3ONO2) through the prism of ab initio simulations of transient-absorption pump-probe spectra.

The photolysis of methyl nitrate (CH3ONO2) UV-excited to the optically bright state is scrutinized by on-the-fly trajectory surface hopping simulations of dynamic observables and transient-absorption pump-probe (TA-PP) spectra. It is found that two major dissociation channels, CH3O + NO2 and CH3O + NO + O, are characterized by the two branches of the stimulated emission signal, which are clearly seen in the total experimentally detectable TA-PP signal. Correlations between the photolysis channels and their TA-PP signatures are established. It is argued that TA-PP spectra may provide valuable information on the multi-channel photolysis mechanisms in similar compounds, and combining ab initio simulations of the dynamic and spectroscopic observables may enhance our understanding of the photodissociation mechanisms and pathways.