Wavepacket propagations for the early time dynamics of proton-coupled electron transfer in the charge-transfer state of NH3Cl complex

A charge-transfer (CT) excited state of NH3Cl, generated by photo-detachment of an electron from the anionic NH3Cl- precursor, can be represented as H2N+-H-Cl- and proceeds to two chemical reactions: one reaction generating NH2 and HCl resulting from a proton transfer (PT) and the other reaction producing NH3 and a Cl atom resulting from an electron transfer (ET); both are coupled to form a typical proton-coupled electron transfer (PCET) process. The early time dynamics of this CT were studied using time-dependent wavepacket propagation on three nonadiabatically coupled electronic states in a reduced three-dimensional space. The electronic states were treated using the XMS-CASPT2/aug-cc-pVTZ ab initio methodology. The population dynamics of the three coupled electronic states were analyzed in detail to reveal the initial stage of the PCET process up to similar to 100 fs, while the branching ratio, chi = PT/(ET+PT), was determined after wavepacket propagations of up to 2000 fs. Another main result is the dependence of chi on the vibration levels of the initial precursor anion and the isotope substitution of the connecting H atom with deuterium and tritium. Our study reveals the detailed microscopic features of the PCET process embedded in the CT state of the NH3Cl complex and certain systematic dependences of the branching ratio chi on the above factors.

Automated summary

The charge-transfer excited state of NH3Cl can undergo a typical proton-coupled electron transfer process through proton transfer and electron transfer. The study reveals that the branching ratio is influenced by the vibration levels of the initial precursor anion and the isotope substitution of the connecting H atom.