Electronic spectra of linear HC$_5$H and cumulene carbene H$_2$C$_5$

TL;DR

This study investigates the electronic spectra of linear HC$_5$H and H$_2$C$_5$, combining experimental observations in neon matrices and gas phase with theoretical calculations to assign spectral transitions.

Contribution

It provides the first experimental and theoretical characterization of the electronic spectra of HC$_5$H and H$_2$C$_5$, including transition assignments and spectral analysis.

Findings

Observation of the $1 ^3\Sigma_u^- ightarrow X^3\Sigma_g^-$ transition in HC$_5$H

Assignment of a new band at 303 nm to H$_2$C$_5$ transition

Use of density functional and CASPT2 methods for spectral assignment

Abstract

The $1 ^3\Sigma_u^- \leftarrow X^3\Sigma_g^-$ transition of linear HC$_5$H (A) has been observed in a neon matrix and gas phase. The assignment is based on mass-selective experiments, extrapolation of previous results of the longer HC$_{2n+1}$H homologues, and density functional and multi-state CASPT2 theoretical methods. Another band system starting at 303 nm in neon is assigned as the $1 ^1 A_1 \leftarrow X ^1 A_1$ transition of the cumulene carbene pentatetraenylidene H$_2$C$_5$ (B).