Spin–orbit coupling and rovibrational structure in the iododiacetylene radical cation by PFI-ZEKE photoelectron spectroscopy

ABSTRACT

The photoelectron spectrum of the X^+ 2Π ← X ¹Σ⁺ photoionising transition of iododiacetylene, HC₄I, has been recorded using pulsed-field-ionisation zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy with partial resolution of the rotational structure. The first adiabatic ionisation energy of HC₄I and the spin–orbit splitting of the X^+ 2Π state of HC₄I⁺ are determined as E^ad_I/(hc) = 74470.7(2) cm⁻¹ and cm⁻¹, respectively. Several vibrational levels of the X^+ 2Π electronic ground state of the HC₄I⁺ cation have been observed. The experimental data are discussed in the realm of a simple three-state charge-transfer model without adjustable parameters which allows for a qualitative description of the electronic structure and spin–orbit coupling in HC₄I⁺ and of the change in bond lengths upon ionisation of HC₄I.

KEYWORDS:

• PFI-ZEKE photoelectron spectroscopy
• spin–orbit interaction
• cations
• Rydberg states

Acknowledgments

The authors thank Urs Hollenstein (ETH Zurich) for experimental help and assistance in the operation of the VUV laser system.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Swiss National Science Foundation under Project No. 200020-159848.