Photophysics and photostability of pyrimidine molecule and its radical cation: a theoretical study

Abstract

ABSTRACTMultistate and multimode vibronic dynamics on first five coupled (S1–S2–S3–S4–S5) electronic states of pyrimidine molecule and first four ( – – –) electronic states of pyrimidine radical cation are investigated with the help of ab initio electronic structure calculations of potential energy surfaces (PESs) and first principle quantum dynamical methods. Excited electronic PESs are generated at the MRCI and Equation of Motion Couple Cluster Single and Double (EOM-CCSD) level of theory. Several low-lying conical intersections among various electronic states are found and their impact on the nuclear dynamics is discussed. The simulation of nuclear motion on the underlying coupled electronic states of pyrimidine molecule and its radical cation is examined by both time-independent and time-dependent quantum mechanical methods. In the latter case, a wave packet propagation-based method within multi-configurational time-dependent Hartree algorithm is employed. The theoretical results are verified with the experimental photoelectron spectroscopy, vacuum ultraviolet spectroscopy and resolved (<10 meV) vibrational energy level spectrum of pyrimidine molecule which has good impact on astrobiology.