Jahn–Teller coupling effects on the lowest energy photoelectron spectrum of adamantane: A theoretical investigation

Abstract

An ab initio quantum dynamics study has been performed here to examine the complex nuclear motions underlying the highly diffuse and irregular vibronic structure of the first photoelectron band of adamantane (Ada). Associated potential energy surfaces of the triply degenerate ground electronic manifold of the adamantane radical cation, subject to T2 ⊗ (e + t2) Jahn–Teller (JT) effect, are established via extensive electronic structure calculations. Subsequently, the nuclear motions on these JT coupled electronic sheets are investigated via wave packet propagations. The theoretical results are in good agreement with the experimental measurements. Larger JT stabilization energy due to T2 ⊗ t2 distortions, compared to T2 ⊗ e distortions, illustrates the dominating role of t2 modes in the symmetry breaking of the initial Td nuclear configuration of adamantane radical cation. The JT effect is also found to play a central role on the highly diffuse, broad, and complex first photoelectron band of Ada. In particular, t2 symmetric ν25 mode (C–C stretching + C–H bending motion) is found to be the origin of the high energy satellite peaks, as well as dominates the vibrational progression underlying the whole band. While the vibrational assignments of some of the major vibronic peaks agree with the available results, renewed assignments are suggested for the remaining peaks.