Spectroscopy on the $A^1\Pi \leftarrow X^1\Sigma^+$ Transition of Buffer-Gas Cooled AlCl

TL;DR

This study combines high-resolution spectroscopy and ab initio calculations to precisely characterize AlCl's electronic structure, confirming its suitability for laser cooling applications.

Contribution

It provides the first detailed experimental and theoretical analysis of AlCl's $A^1\Pi ightarrow X^1\Sigma^+$ transition, with high-precision spectroscopic constants and Franck-Condon factor estimation.

Findings

High-resolution spectral data matches ab initio calculations.

Estimated Franck-Condon factor of 99.88%.

AlCl is suitable for laser cooling.

Abstract

Aluminum monochloride (AlCl) has been proposed as an excellent candidate for laser cooling. Here we present absorption spectroscopy measurements on the $A^1\Pi \leftarrow X^1\Sigma^+$ transition in AlCl inside a cryogenic helium buffer-gas beam cell. The high resolution absorption data enables a rigorous, quantitative comparison with our high-level ab initio calculations of the electronic and rovibronic energies, providing a comprehensive picture of the AlCl quantum structure. The combination of high resolution spectral data and theory permits the evaluation of spectroscopic constants and associated properties, like equilibrium bond length, with an order of magnitude higher precision. Based on the measured molecular equilibrium constants of the $A^1\Pi$ state, we estimate a Franck-Condon factor of the $A^1\Pi \leftarrow X^1\Sigma^+$ of 99.88%, which confirms that AlCl is amenable to laser cooling.