Laser-induced, blackbody-radiation-assisted rovibrational cooling of symmetric-top molecular ions: NH₃⁺ and ND₃⁺

Sinha, Archisman, Heazlewood, Brianna R ORCID: 0000-0003-2073-4004 and Deb, Nabanita (2026) Laser-induced, blackbody-radiation-assisted rovibrational cooling of symmetric-top molecular ions: NH₃⁺ and ND₃⁺ JOURNAL OF CHEMICAL PHYSICS, 164 (22). ISSN 0021-9606, 1089-7690

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Abstract

Quantum-state preparation of molecular ions is a prerequisite for precision spectroscopy and controlled studies of cold ion–molecule dynamics. While such control has been extensively developed for diatomic ions and proposed for linear polyatomic ions, corresponding strategies for symmetric-top molecular ions remain largely unexplored. We present a theoretical investigation of blackbody-radiation (BBR)–assisted rovibrational dynamics and laser cooling in the symmetric-top ions NH 3 + and ND 3 +, prepared in specific rovibrational states by resonance enhanced multiphoton ionization of the neutral precursor. State-resolved radiative lifetimes and equilibration times are computed, revealing that vibrationally excited states decay rapidly, while the ground-state redistribution is dominated by slow BBR-driven rovibrational transitions, as pure rotational transitions are forbidden in the nonpolar NH 3 + and ND 3 + ions. BBR-assisted laser pumping via the ν <inf>2</inf> umbrella-bending mode efficiently cools rotational levels within fixed K manifolds; however, ΔK = 0 selection rules induce a bottleneck, limiting access to the absolute rovibrational ground state for some initially prepared states. Isotopic substitution to ND 3 + slows the redistribution dynamics due to the lower transition dipole moment. At room temperature, these cooling schemes yield > 90% and >85% of the population in selected rovibrational states of the NH 3 + and ND 3 + ions, respectively. In contrast, at temperatures below 100 K, BBR-induced redistribution is strongly suppressed for ions initially produced in the rovibrational ground state, effectively freezing the population for extended storage times. The schemes presented here provide a practical pathway for preparing state-selected molecular ions for precision spectroscopy and controlled ion–molecule reaction studies.

Item Type:	Article
Uncontrolled Keywords:	51 Physical Sciences, 34 Chemical Sciences, 5102 Atomic, Molecular and Optical Physics, 3406 Physical Chemistry
Divisions:	Faculty of Science & Engineering Faculty of Science & Engineering > School of Physical Sciences Faculty of Science & Engineering > School of Physical Sciences > Physics
Depositing User:	Symplectic Admin
Date Deposited:	10 Jul 2026 07:06
Last Modified:	10 Jul 2026 07:06
DOI:	10.1063/5.0331866
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3199348
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