# Reassigning the CaH$^+$ 1$^{1}\Sigma\rightarrow$ 2$^{1}\Sigma$ vibronic transition with CaD$^+$

## TL;DR

This study revises the vibronic transition assignment in CaH$^+$ by observing similar transitions in CaD$^+$, revealing discrepancies with theoretical predictions and refining molecular energy level understanding.

## Contribution

It provides the first experimental observation of vibronic transitions in CaD$^+$ and revises the vibronic level assignment for CaH$^+$ based on these findings.

## Key findings

- Revised vibronic level assignment for CaH$^+$.
- Discrepancy of about 700 cm$^{-1}$ with CASPT2 calculations.
- Successful observation of vibronic transitions in CaD$^+$.

## Abstract

We observe vibronic transitions in CaD$^+$ between the 1$^{1}\Sigma$ and 2$^{1}\Sigma$ electronic states by resonance enhanced multiphoton photodissociation spectroscopy in a Coulomb crystal. The vibronic transitions are compared with previous measurements on CaH$^+$. The result is a revised assignment of the CaH$^+$ vibronic levels and a disagreement with CASPT2 theoretical calculations by approximately 700 cm$^{-1}$.