Direct Evidence of the Benzylium and Tropylium Cations as the two long-lived Isomers of C7H7+

TL;DR

This study provides direct infrared spectral evidence confirming benzylium and tropylium as the only long-lived isomers of C7H7+ and compares experimental data with theoretical calculations.

Contribution

It presents the first full mid-infrared vibrational spectrum of C7H7+ with isomer-specific assignments, clarifying the isomeric structure of this ion.

Findings

Benzylium and tropylium are the only long-lived isomers of C7H7+.

Spectral features match density functional theory calculations.

No other isomeric forms of C7H7+ are involved.

Abstract

Disentangling the isomeric structure of C7H7+ is a longstanding experimental issue. We report here the full mid-infrared vibrational spectrum of C7H7+ tagged with Ne obtained with infrared-predissociation spectroscopy at 10 K. Saturation depletion measurements were used to assign the contribution of benzylium and tropylium isomers and demonstrate that no other isomer is involved. Recorded spectral features compare well with density functional theory calculations. This opens perspectives for a better understanding and control of the formation paths leading to either tropylium or benzylium ions.