Roaming mediated nonadiabatic dynamics in molecular hydrogen elimination from propane at 157nm

Highlights: • Our work reveals the occurrence of roaming mediated nonadiabtic pathways for the elimination of molecular hydrogen from propane at 157 nm. • 1,2- and 1,3-molecular hydrogen eliminations, exclusively follow roaming (of partially dissociated H atom) mediated nonadiabatic pathway (S₁ → S₀) to the ground electronic state followed by an atomic hydrogen abstraction from another carbon atom in the ground singlet (S₀) state. • 1,1- and 2,2-molecular hydrogen eliminations on the other hand, proceed either adiabatically on first excited singlet (S₁) electronic state or through the conventional internal conversion S₁ → S₀ followed by direct two-body fragmentation in the ground singlet (S₀) state, with equal probability. The photofragmentation dynamics study using Tully's fewest switches trajectory surface hopping calculations, based on MRCIS(6, 6)/6-31++G∗∗ potential energy surfaces, energy gradients and nonadiabatic couplings, reveals the occurrence of roaming mediated nonadiabatic pathways for the elimination of molecular hydrogen from propane at 157 nm. 1,2- and 1,3-molecular hydrogen eliminations, the minor dissociation channels, exclusively follow roaming (of partially dissociated H atom) mediated nonadiabatic pathway (S₁ → S₀) to the ground electronic state followed by an atomic hydrogen abstraction from another carbon atom in the ground singlet (S₀) state. 1,1- and 2,2-molecular hydrogen eliminations on the other hand, the major dissociation processes, proceed either adiabatically in the first excited singlet (S₁) electronic state or through the internal conversion S₁ → S₀ followed by direct two-body fragmentation in the ground singlet (S₀) state, with equal probability.