We constructed an analytic diabatic potential energy matrix (DPEM) that describes the N-H photodissociation of methylamine; the electronic state space includes the ground and first excited singlet states. The input for the fit was calculated by extended multi-state complete active space second-order perturbation theory. The data were diabatized using the dipole-quadrupole diabatization method in which we incorporated a coordinate-dependent weighting scheme for the contribution of the quadrupole moments. To make the resulting potential energy surfaces semiglobal, we extended the anchor points reactive potential method, a multiscale approach that assigns the internal coordinates to categories with different levels of computational treatment. Key aspects of the adiabatic potential energy surfaces obtained by diagonalizing the DPEM agree with the available experimental and theoretical data at energies relevant for photochemical studies.
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The authors thank Chad E. Hoyer, Zolt??n Varga, Siriluk Kanchanakungwankul, Linyao Zhang, Yinan Shu, and the late Steven L. Mielke for helpful discussions. We are grateful to Elliot Bernstein for helpful discussion of the experiments. This work was supported, in part, by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award No. DE-SC0015997.
© 2020 Author(s).