Probing the Electronic Manifold of MgCl with Millimeter-Wave Spectroscopy and Theory: (3)2Σ+ and (4)2Σ+ States

T J Herman; R Ravi; M S Schuurman; N J DeYonker; R W Field; L M Ziurys

doi:10.1021/acs.jpca.4c05458

Probing the Electronic Manifold of MgCl with Millimeter-Wave Spectroscopy and Theory: (3)²Σ⁺ and (4)²Σ⁺ States

J Phys Chem A. 2024 Nov 21;128(46):9893-9903. doi: 10.1021/acs.jpca.4c05458. Epub 2024 Nov 13.

Authors

T J Herman¹, R Ravi¹, M S Schuurman², N J DeYonker³, R W Field⁴, L M Ziurys^{1

5}

Affiliations

¹ Department of Chemistry and Biochemistry, University of Arizona, 1305 East Fourth Street, Tucson, Arizona 85719, United States.
² Department of Chemistry and Biomolecular Sciences, National Research Council of Canada, Ottawa, ON K1A 0R6,Canada.
³ Department of Chemistry, University of Memphis, Memphis, Tennessee 38152, United States.
⁴ Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
⁵ Department of Astronomy and Steward Observatory, University of Arizona, 1305 East Fourth Street, Tucson, Arizona 85719, United States.

PMID: 39535137
PMCID: PMC11587948 (available on 2025-11-13)
DOI: 10.1021/acs.jpca.4c05458

Abstract

The millimeter/submillimeter spectrum of magnesium chloride (MgCl) has been observed in two new electronic excited states, (3)²Σ⁺ and (4)²Σ⁺, using direct absorption methods. The molecule was synthesized in a mixture of Cl₂, argon, and magnesium vapor. For the (3)²Σ⁺ state, multiple rotational transitions were measured in the v = 0 level for all six isotopologues (²⁴Mg³⁵Cl, ²⁴Mg³⁷Cl, ²⁵Mg³⁵Cl, ²⁵Mg³⁷Cl, ²⁶Mg³⁵Cl, and ²⁶Mg³⁷Cl), as well as up to v = 13 for ²⁴Mg³⁵Cl. For the (4)²Σ⁺ state, less intense spectra were recorded for ²⁴Mg³⁵Cl (v = 0-2). Equilibrium rotational parameters were determined for both states for ²⁴Mg³⁵Cl, as well as rotational constants and ²⁵Mg hyperfine parameters for the other isotopologues. A perturbation was observed between rotational levels of the two states due to an avoided crossing. Computations were also carried out at the CASPT2 and MRCISD+Q levels, and the resulting bond lengths for (3)²Σ⁺ and (4)²Σ⁺ states agree well with the experimental values of r_e = 2.536 and 2.361 Å. The computations show that the (3)²Σ⁺ state has a double-well potential; however, the state behaves as a single well with unperturbed vibrational levels up to v = 13 due to nonadiabatic interactions with the (4)²Σ⁺ state.