Overtone Transition $2\nu_1$ of $\text{HCO}^+$ and $\text{HOC}^+$: Origin, Radiative Lifetime, Collisional Quenching

TL;DR

This study measures the overtone vibrational transition of HCO+ and HOC+ ions using a novel laser-induced reaction technique, determining their spectral origins, radiative lifetimes, and collisional quenching rates in a cryogenic ion trap.

Contribution

It introduces a mass-selective ejection method for background-free spectra and provides new measurements of vibrational transition origins, lifetimes, and quenching rates for HCO+ and HOC+ ions.

Findings

Band origins at 6078.68 and 6360.18 cm⁻¹ for HCO+ and HOC+

Radiative lifetimes of 1.53 ms and 1.22 ms for the overtone states

Collisional quenching rates with He, H₂, N₂ estimated

Abstract

We present spectra of the first overtone vibration transition of $\text{C-H}$/$\text{O-H}$ stretch ($2\nu_1$) in $\text{HCO}^+$ and $\text{HOC}^+$, recorded using a laser induced reaction action scheme inside a cryogenic 22 pole radio frequency trap. Band origins have been located at 6078.68411(19) and 6360.17630(26) $\text{cm}^{-1}$, respectively. We introduce a technique based on mass selective ejection from the ion trap for recording background free action spectra. Varying the number density of the neutral action scheme reactant ($\text{CO}_2$ and Ar, respectively) and collisional partner reactant inside the ion trap, permitted us to estimate the radiative lifetime of the state to be 1.53(34) and 1.22(34) ms, respectively, and the collisional quenching rates of $\text{HCO}^+$ ($2\nu_1$) with He, H$_2$, and N$_2$.