Understanding Photolysis of CH _\bf3 ONO _\bf2 with on-the-fly Nonadiabatic Dynamics Simulation at the ADC(2) Level

The nonadiabatic dynamics of methyl nitrate (CH _3 ONO _2 ) is studied with the on-the-fly trajectory surface hopping dynamics at the ADC(2) level. The results confirmed the existence of the ultrafast nonadiabatic decay to the electronic ground state. When the dynamics starts from S _1 and S _2 , the photoproducts are CH _3 O+NO _2 , consistent with previous results obtained from the experimental studies and theoretical dynamics simulations at more accurate XMS-CASPT2 level. The photolysis products are CH _3 O+NO _2 at the ADC(2) level when the dynamics starts from S _3 , while different photolysis products were obtained in previous experimental and theoretical works. These results demonstrate that the ADC(2) method may still be useful for treating the photolysis mechanism of CH _3 ONO _2 at the long-wavelength UV excitation, while great caution should be paid due to its inaccurate performance in the description of the photolysis dynamics at the short-wavelength UV excitation. This gives valuable information to access the accuracy when other alkyl nitrates are treated at the ADC(2) level.