Charge-Transfer-Induced Predissociation in Rydberg States of Molecular Cations: MgAr+
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2021-08-12
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Journal Article
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Abstract
Very little is known about the Rydberg states of molecular cations, i.e., Rydberg states having a doubly charged ion core. With the example of MgAr+, we present general features of the structure and dynamics of the Rydberg states of molecular cations, which we find are subject to the process of charge-transfer-induced predissociation. Our study focuses on the spectrum of low-n Rydberg states with potential-energy functions associated with the Mg+(3d and 4s) + Ar(S-1(0)) dissociation asymptotes. In particular, we have recorded spectra of the 3d pi(Omega') (Omega' = 1/2, 3/2) Rydberg states, extending from the lowest (v' = 0) vibrational levels to their dissociation limits. This spectral range encompasses the region where the onset of predissociation by interaction with the mostly repulsive (2)Sigma and (2)Pi charge-transfer states associated with the Mg(3s(2)) + Ar+(P-2(1/2,3/2)) dissociation asymptotes is observed. This interaction leads to very strong perturbations of the 3d pi Rydberg states of MgAr+, revealed by vibrational progressions exhibiting large and rapid variations of the vibrational intervals, line widths, and spin-orbit splittings. We attribute the anomalous sign and magnitude of the spin-orbit coupling constant of the 3dp state to the interaction with a (2)Pi Rydberg state correlating to the Mg+(4p) + Ar(S-1(0)) dissociation limit. To analyze our spectra and elucidate the underlying process of charge-transfer-induced predissociation, we implemented a model that allowed us to derive the potential-energy functions of the charge-transfer states and to quantitatively reproduce the experimental results. This analysis characterizes the main features of the dynamics of the Rydberg series converging to the ground state of MgAr2+. We expect that the results and analysis reported here are qualitatively valid for a broader range of singly charged molecular cations, which are inherently prone to charge-transfer interactions.
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125 (31)
Pages / Article No.
6681 - 6696
Publisher
American Chemical Society
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03736 - Reiher, Markus / Reiher, Markus
03449 - Merkt, Frédéric / Merkt, Frédéric
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200478 - Precision measurements with cold molecules: Rydberg states, ions and photoionization (SNF)
743121 - Cold Ion Chemistry - Experiments within a Rydberg Orbit (EC)
743121 - Cold Ion Chemistry - Experiments within a Rydberg Orbit (EC)