OH⁺IN ASTROPHYSICAL MEDIA: STATE-TO-STATE FORMATION RATES, EINSTEIN COEFFICIENTS AND INELASTIC COLLISION RATES WITH He

Abstract

The rate constants required to model the OH + observations in different regions of the interstellar medium have been determined using state of the art quantum methods. First, state-to-state rate constants for the H 2 (v = 0, J = 0, 1)+ O + ( 4 S) → H + OH + (X 3 Σ − , v ′ , N ) reaction have been obtained using a quantum wave packet method. The calculations have been compared with time-independent results to asses the accuracy of reaction probabilities at collision energies of about 1 meV. The good agreement between the simulations and the existing experimental cross sections in the 0.01−1 eV energy range shows the quality of the results. The calculated state-to-state rate constants have been fitted to an analytical form. Second, the Einstein coefficients of OH + have been obtained for all astronomically significant ro-vibrational bands involving the X 3 Σ − and/or A 3 Π electronic states. For this purpose the potential energy curves and electric dipole transition moments for seven electronic states of OH + are calculated with ab initio methods at the highest level and including spin-orbit terms, and the rovibrational levels have been calculated including the empirical spin-rotation and spin-spin terms. Third, the state-to-state rate constants for inelastic collisions between He and OH + (X 3 Σ − ) have been calculated using a time-independent close coupling method on a new potential energy surface. All these rates have been implemented in detailed chemical and radiative transfer models. Applications of these models to various astronomical sources show that inelastic collisions dominate the excitation of the rotational levels of OH + . In the models considered the excitation resulting from the chemical formation of OH + increases the line fluxes by about 10 % or less depending on the density of the gas.

Modeling Quantum Kinetics in Ion Traps: State‐changing Collisions for OH+() Ions with He as a Buffer Gas

“…The calculations for a new PES were recently carried out again in a later study, where the fuller Jacobi space was considered. The radial distances corresponded to 57 R values between 2.75 a 0 and 32 a 0 , with a varying step as the earlier calculations.…”

“…A detailed study of such reaction has been carried out recently in a comprehensive computational analysis of its rates with their applications tovarious astronomical sources, indicating the importance of forming OH + in excited rovibrational states. This work also carried out the evaluation of a new potential energy surface (PES) involving OH + ( ) and He atoms, together with a selection of inelastic collision rates for that system.…”

Quantum and quasi-classical calculations for the S+ + H2(v,j) → SH+(v′,j′) + H reactive collisions

“…In addition, we study the state-to-state dynamics, to provide state-to-state cross sections to be used to determine the emission from excited rotational states, as recently done for CH + [12] and OH + [13].…”

Book of Proceedings: Ninth Workshop, Sunny Beach, Bulgaria, May 30 - June 3, 2017

“…In this study, total reaction rate constants and cross sections obtained for the reaction [Gómez-Carrasco et al, 2014] …”

“…It has been found that the release of modest amount H 2 gas can produce significant perturbations in the ionosphere and protonosphere [Bernhardt et al, 1975]. Also the effect on ionosphere of O + and H 2 was separately investigated by them and no attempt was made the effects on the earth ionosphere by combining kinetic theorybased models with the cross sections in the 0.02-0.1 eV collision energy range and state to state rate constants values for the O + + H 2 → OH + + H reaction that have been obtained using a quantum wave packet method.In this study, total reaction rate constants and cross sections obtained for the reaction [Gómez-Carrasco et al, 2014] …”