Study of non‐adiabatic interactions among low‐lying electronic states of HeH₂⁺ with its implication in its dissociation into various species

Abstract

Possible interplay of various atomic and molecular systems like He+, He, H+, H, H2+, H2, HeH+, HeH2+ in the interstellar spaces in various phases of the creation and development of the universe as well as in the present interstellar spaces have been the subject of experimental and theoretical investigations for quite a long period. A chemical network involving these species has been considered. The molecular system HeH2+, being a weakly bound species, may readily give the dissociation products (H, HeH+), (He, H2+), (He+, H2) and (He, H, H+) through different dissociation channels, as has been argued from the contour diagram of the ground as well as non‐adiabatically interacting excited electronic state. A seam of Conical Intersections (CI) between two lowest excited states of linear HeH2+, as a result of non‐adiabatic interactions, has been demonstrated for the first time, through calculation and plot of non‐adiabatic coupling term (NACT) between these two states. Calculations of NACT's, followed by construction of the adiabatic‐to‐diabatic transformation (ADT) angles, ADT matrix and calculation of topological (Berry) phases have been presented to confirm the presence of Jahn‐Teller(JT) CI in two representative configuration spaces(CS) in this seam: (i) one away from the equilibrium geometry hosting JT‐CI between two excited states 22A′ and 32A′ and (ii) another CS near the equilibrium geometry hosting JT‐CI between excited states 22A′ and 32A′ as well as a closely spaced JT‐CI between excited states 32A′ and 42A′. Suitable diabatizations have been performed for a range of CS covering these two CI, which help in understanding several dissociation channels of HeH2+ involving the above mentioned excited states, leading to an increase in the yield of dissociation products (He, H, H+). Distribution of Mulliken partial charges, as obtained from Mulliken population analysis have been analyzed for justifying the existence of HeH2+, the possibility of different dissociation products of HeH2+ in different dissociation channels as well as the justification of the CI‐induced charge transfer in excited states.

High-resolution electronic and vibrational spectroscopy of small-to-medium sized molecules with ab initio potential energy surface

“…This collision also leads to HeH + 2 as an intermediate complex [39,128]. Since its discovery in a planetary Nebula [108], HeH + gained renewed attention and many theoretical studies have been performed on the dynamics of HeH + and HeH + 2 [40,[133][134][135][136][137]. The structural features of HeH + 2 and reactive collision dynamics for this system have been reviewed recently by Sathyamurthy et al [138].…”

Beyond Born–Oppenheimer Constructed Diabatic Potential Energy Surfaces for HeH2+

“…Gupta et al investigated the nonadiabatic coupling between the ground and the first three excited states for the system and computed the adiabatic-to-diabatic transformation (ADT) angle to show the CIs between the ground and the first excited state in C 2 v geometries and between the first and the second excited state in collinear geometry. Mondal et al identified a seam of CIs between the first two excited states. Ravi et al extended the earlier study by Gupta et al by performing MR-CISD level calculations using the aug-cc-pVTZ basis set and identified ten CIs for the system .…”