# High-resolution photoelectron-spectroscopic investigation of the H$_2$O$^+$ cation in its ${\mathrm {\tilde A^+}}$ electronic state

## TL;DR

This study uses high-resolution photoelectron spectroscopy to analyze the rotational structure of the H$_2$O$^+$ cation's ${ ilde A^+}$ electronic state, providing detailed spectral assignments and insights into its vibronic states.

## Contribution

It presents the first high-resolution spectral analysis of the ${ ilde A^+}$ state of H$_2$O$^+$, including rotational assignments based on previous studies and selection rules.

## Key findings

- Rotational structure observed in multiple vibronic bands.
- Assignments made for $ ilde{
m A}^+$ vibronic states $
m \Pi(080)$, $
m \Sigma(070)$, $
m \Pi(060)$.
- Tentative assignment for the $
m \Sigma(030)$ state.

## Abstract

The photoelectron spectrum of water has been recorded in the vicinity of the ${\mathrm {\tilde A^+}}$ $\leftarrow$ $\tilde{\mathrm{X}}$ transition between 112 000 and 116 000 cm$^{-1}$ (13.89-14.38 eV). The high-resolution allowed the observation of the rotational structure of several bands. Rotational assignments of the transitions involving the $\Pi(080)$, $\Sigma(070)$ and $\Pi(060)$ vibronic states of the $\tilde{\mathrm{A}}^+$ electronic state are deduced from previous studies of the $\tilde{\mathrm{A}}^+ - \tilde{\mathrm{X}}^+$ band system of H$_2$O$^+$ (Lew, Can. J. Phys. 54, 2028 (1976) and Huet et al., J. Chem. Phys. 107, 5645 (1997)) and photoionization selection rules. The transition to the $\Sigma(030)$ vibronic state is tentatively assigned.