Rovibrational spectroscopy of the CH$^+$-He and CH$^+$-He$_4$ complexes

TL;DR

This study uses cryogenic ion trapping and IR spectroscopy to analyze the structure of CH$^+$ complexes with helium, revealing their geometric configurations through vibrational spectra at 4 K.

Contribution

It provides the first spectroscopic characterization of CH$^+$-He and CH$^+$-He$_4$ complexes, confirming their geometries via vibrational transition patterns.

Findings

CH$^+$-He has a T-shaped, near prolate top structure.

CH$^+$-He$_4$ exhibits an oblate top structure with parallel transitions.

Infrared spectra confirm the molecular geometries at cryogenic temperatures.

Abstract

A cryogenic 22-pole ion trap apparatus is used in combination with a table-top pulsed IR source to probe weakly bound CH$^+$-He and CH$^+$-He$_4$ complexes by predissociation spectroscopy at 4 K. The infrared photodissociation spectra of the C-H stretching vibrations are recorded in the range of 2720-2800 cm$^{-1}$. The spectrum of CH$^+$-He exhibits perpendicular transitions of a near prolate top with a band origin at 2745.9 cm$^{-1}$, and thus confirms it to have a T-shaped structure. For CH$^+$-He$_4$, the C-H stretch along the symmetry axis of this oblate top results in parallel transitions.