Abstract
In high orbital angular momentum (ℓ ≥ 3) Rydberg states, the centrifugal barrier hinders the close approach of the Rydberg electron to the ion-core. As a result, these core-nonpenetrating Rydberg states can be well described by a simplified model in which the Rydberg electron is only weakly perturbed by the long-range electric properties (i.e., multipole moments and polarizabilities) of the ion-core. We have used a long-range model to describe the vibrational autoionization dynamics of high-ℓ Rydberg states of nitric oxide (NO). In particular, our model explains the extensive angular momentum exchange between the ion-core and the Rydberg electron that had been previously observed in vibrational autoionization of f (ℓ = 3) Rydberg states. These results shed light on a long-standing mechanistic question around these previous observations and support a direct, vibrational mechanism of autoionization over an indirect, predissociation-mediated mechanism. In addition, our model correctly predicts newly measured total decay rates of g (ℓ = 4) Rydberg states because for ℓ ≥ 4, the non-radiative decay is dominated by autoionization rather than predissociation. We examine the predicted NO+ ion rotational state distributions generated by vibrational autoionization of g states and discuss applications of our model to achieve quantum state selection in the production of molecular ions.
Highlights
Among the most compelling new topics at the intersection of chemistry and physics is the study of chemical reactions and molecular collisions at extremely cold temperatures in which quantum state-specific behavior is resolved.1–3 A diverse range of experimental techniques encompassing beams, traps, and cryogenic matrices enable study of collision energies from a few Kelvins to submilliKelvins
We calculated the nitric oxide (NO)+ ion rotational state distributions that result from vibrational autoionization of selected f Rydberg states by summing the rates of all outgoing electron partial waves that result in formation of a given final rotational state of the ion
The model predictions are compared to the experimental results for v = 1 and v = 2 f Rydberg states from Refs. 11 and 13, respectively
Summary
Among the most compelling new topics at the intersection of chemistry and physics is the study of chemical reactions and molecular collisions at extremely cold temperatures in which quantum state-specific behavior is resolved. A diverse range of experimental techniques encompassing beams, traps, and cryogenic matrices enable study of collision energies from a few Kelvins to submilliKelvins (see Ref. 3 and references therein). Beyond control of the collision energy, resolution of individual quantum states of both reactants and products has led to some of the most detailed pictures of chemical reactions to date.. Beyond control of the collision energy, resolution of individual quantum states of both reactants and products has led to some of the most detailed pictures of chemical reactions to date.4,5 In such quantum-stateresolved studies of chemical reactivity, the generation of reactant molecules or ions in single quantum states is one of the greatest challenges, and only a few systems have been experimentally realized far.. Autoionization refers to the spontaneous ionization of a neutral Rydberg molecule when the total energy of a Rydberg electron around a vibrationally excited ion-core exceeds the ionization energy of the vibrationless level in one or more rotational states. In recent applications, this approach has only succeeded in producing molecular ions distributed over at least three final rotational states. earlier work demonstrated that rotational quantum number changes as large as four quanta are possible in the autoionization of certain Rydberg series, upending the simple picture of the Rydberg electron being released without perturbation of the ion-core
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