Photoelectron spectroscopic study of the E ⊗ e Jahn-Teller effect in the presence of a tunable spin-orbit interaction. II. Rovibronic analysis of the 2E ground state of CH3CI+
The PFI-ZEKE photoelectron spectrum of the CH3Cl+ ? E ← CH3Cl ? transition was recorded in the range 90900-93400 cm-1 following single-photon excitation from the ground state. The spectrum consists of well-resolved spin-vibronic bands, some of which with partially resolved rotational structure, and provides new information on the combined effects of the Jahn-Teller and spin-orbit interaction in the ? E ground state of CH3Cl+. The analysis of its spin-rovibronic structure reveals a weak linear Jahn-Teller effect along the H3C-Cl bending e mode (ν6) and enabled the derivation of Jahn-Teller coupling constants along ν6, rotational constants, and spin-orbit interaction parameters for the ? E ground state of CH3Cl+. The Jahn-Teller effect is dynamical in the ground state of CH3Cl+ and the photoelectron spectrum does not provide evidence for a reduction of the molecular symmetry to Cs symmetry. Weak rotational satellite bands were observed in transitions to several excited vibrational levels of CH3Cl+ and interpreted in terms of the spin-rovibronic photoionization selection rule ? derived in the analysis of the photoelectron spectrum of CH3I (M. Grütter, J. M. Michaud and F. Merkt, J. Chem. Phys. 134, 054308 (2011)). Compared to the ground state of HCl+ ( ? cm-1), the spin-orbit splitting is strongly reduced to ? cm-1. The reduction is primarily attributed to an electronic effect ? and, to a lesser extent, to the quenching of the spin-orbit interaction by the Jahn-Teller effect ? .