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⁺

Abstract

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 C_s 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 .

Keywords:

• Jahn–Teller effect
• spin–orbit interaction
• PFI-ZEKE photoelectron spectroscopy
• methyl chloride

Acknowledgements

This work was supported financially by the Swiss National Science Foundation under project Nr. 200020-135342.