Time-dependent quantum wave-packet description of H and D atom tunneling in N-H and N-D photodissociation of methylamine and methylamine-d2.

The degree to which tunneling through a barrier in the N-H and N-D photodissociation channels of methylamine (CH3NH2) and its deuterated variant (CH3ND2), respectively, plays a role was investigated by time-dependent quantum wave-packet dynamics calculations. Two dimensional potential energy surfaces (PESs) of methylamine, presenting the N-H stretch and the HNC bend, were constructed employing multireference ab initio electronic-structure methods, allowing full description of the H motion on the HC-NH2 plane. The time-dependent Schrödinger equation was solved employing the Fourier method for calculating the Hamiltonian operation together with the Chebychev polynomial expansion of the evolution operator. The results show that tunneling and decay to vibrational resonant states on the first excited electronic PES are faster for the H atom than for the D. The decay into two of the resonant states found on the first PES strongly depends on the initially excited vibrational state on the ground electronic PES.