Infrared spectrum of H5+and D5+: The simplest shared-proton model

Abstract

We present a two-dimensional collinear, adiabatic model to describe the motion of a proton in between two hydrogen molecules which adjust their elongation to trace a minimum-energy path. Together with bound states, the predissociative, vibrationally excited states involved in the electric dipole transitions are characterized. The main qualitative features of the infrared spectra of H 5 + and its deuterated variant are discussed, and the effect of the temperature of the clusters is analyzed. To just account for the proton transfer between the two H 2 moieties, we present an extremely simplified two-dimensional (2D) model which incorporates the effect of the temperature.Considering three collinear masses M 1 -M 0 -M 2 , denoting by d 1 and d 2 , the distances from the central mass to the extreme ones, and employing the coordinates R = d 1 + d 2 (0 R ∞) and r = d 1 − d 2 (−R r R) the kinetic energy operator in the center of mass system becomeŝ

Simulation of the infrared predissociation spectra of H5+

“…The discrepancies with the experimental results [25] could be attributed to the use of a normal-mode basis set to describe large-amplitude motions, without taking into account the predissociation dynamics of the excited levels reached by infrared absorption. Due to the difficulty of including full dimensions and predissociation dynamics, recently a simple shared-proton model has been developed [52] using two coordinates describing the motion of the central proton between two H 2 molecules, providing a reasonable physical assignment of the experimental bands [25]. In this work this simple model is extended to more degrees of freedom, using the same PES [40], with the aim of characterizing the resonances and the main vibrations involved.…”

“…The close analogy between the vibrational progressions obtained in the 3D, 5D, and 7D models indicates that the 3D model already catches some of the most important ingredients of the spectrum. These dimensions correspond to a proton-shared model [52], with a central proton vibrating in between the two H 2 subunits, producing changes in the electric dipole responsible for the transitions.…”

“…This is equivalent to the 2D treatment used before [52], in which these coordinates were further modified to account for the symmetric and antisymmetric vibrations. Here we keep these coordinates to progressively include more dimensions in the model.…”

Dynamically biased statistical model for the ortho/para conversion in the ${\rm H}_2 + {\rm H}_3^+$H2+H3+ → ${\rm H}_3^{+} +$H3++ H2 reaction

“…[59][60][61]65 If the hypothesis discussed above is true, there may be some differences in the broadening of the resonances near the dissociation threshold as a function of the total angular momentum excitation, and this could be probably measured by changing the experimental rotational temperature of the experiments. Also, there have been several theoretical simulations on this infrared predissociation spectra, 44,61,62 but they use either approximate methods or reduced dimensionality models which need to be improved to account for the narrow resonances at high J with enough accuracy to extract information relevant for the transition between statistical and direct regimes in the collisions discussed in this work.…”

“…The experimental value at 135 K of Crabtree et al 17 is much lower than the one obtained here, and very close to the statistical limit. In order to improve the present results, quantum cal- [59][60][61] Recently, several quantum approximate and/or reduced dimensionality simulations of the predissociation spectrum have been performed 44,61,62 providing some physical assignment. The agreement between experiment and theory is still quite poor, what demonstrate the need of designing new quantum methods to include all degrees of freedom and the permutation symmetry in this problem.…”