Computational Sciences - Research Publications
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Item HeH+Collisions with H2: Rotationally Inelastic Cross Sections and Rate Coefficients from Quantum Dynamics at Interstellar Temperatures(American Chemical Society, 2022-04-01T00:00:00) Giri, K.; Gonz�lez-S�nchez, L.; Biswas, Rupayan; Yurtsever, E.; Gianturco, F.A.; Sathyamurthy, N.; Lourderaj, U.; Wester, R.We report for the first time an accurate ab initio potential energy surface for the HeH+-H2system in four dimensions (4D) treating both diatomic species as rigid rotors. The computed ab initio potential energy point values are fitted using an artificial neural network method and used in quantum close coupling calculations for different initial states of both rotors, in their ground electronic states, over a range of collision energies. The state-to-state cross section results are used to compute the rate coefficients over a range of temperatures relevant to interstellar conditions. By comparing the four dimensional quantum results with those obtained by a reduced-dimensions approach that treats the H2molecule as an averaged, nonrotating target, it is shown that the reduced dimensionality results are in good accord with the four dimensional results as long as the HeH+molecule is not initially rotationally excited. By further comparing the present rate coefficients with those for HeH+-H and for HeH+-He, we demonstrate that H2molecules are the most effective collision partners in inducing rotational excitation in HeH+cation at interstellar temperatures. The rotationally inelastic rates involving o-H2and p-H2excitations are also obtained and they turn out to be, as in previous systems, orders of magnitude smaller than those involving the cation. The results for the H2molecular partner clearly indicate its large energy-transfer efficiency to the HeH+system, thereby confirming its expected importance within the kinetics networks involving HeH+in interstellar environments. � 2022 American Chemical Society. All rights reserved.Item Efficiency of rovibrational cooling of HeH+ by collisions with He: Cross sections and rate coefficients from quantum dynamics(American Institute of Physics Inc., 2021-10-15T00:00:00) Gianturco, F.A.; Giri, K.; Gonz�lez-S�nchez, L.; Yurtsever, E.; Sathyamurthy, N.; Wester, R.By extending an earlier study [Gianturco et al., J. Chem. Phys. 154, 054311 (2021)] on the purely rotational excitation of HeH+ by He atoms, we report in this paper integral cross sections and rate coefficients for rovibrational excitation and de-excitation processes in HeH+ due to collisions with He. The data were obtained using a new ab initio potential energy surface that includes the vibrational degree of freedom. The results are compared with those computed using the earlier potential energy surface by Panda and Sathyamurthy [J. Phys. Chem. A 107, 7125 (2003)] that additionally accounts for the proton-exchange reaction between HeH+ and He. It is shown that the exchange channel contributes nearly as much as the inelastic channel to the vibrational excitation and de-excitation processes and that the total rate constants pertaining to the purely inelastic processes are largely of the same magnitude as those obtained when both inelastic and reactive channels are included in the dynamics. The inelastic rovibrational rate coefficients involving this astrophysical cation are also found to be much larger than those obtained for anions present in similar interstellar environments. � 2021 Author(s).Item Energy-transfer quantum dynamics of HeH+with He atoms: Rotationally inelastic cross sections and rate coefficients(American Institute of Physics Inc., 2021-02-04T00:00:00) Gianturco, F.A.; Giri, K.; Gonz�lez-S�nchez, L.; Yurtsever, E.; Sathyamurthy, N.; Wester, R.Two different ab initio potential energy surfaces are employed to investigate the efficiency of the rotational excitation channels for the polar molecular ion HeH+ interacting with He atoms. We further use them to investigate the quantum dynamics of both the proton-exchange reaction and the purely rotational inelastic collisions over a broad range of temperatures. In current modeling studies, this cation is considered to be one of the possible cooling sources under early universe conditions after the recombination era and has recently been found to exist in the interstellar medium. The results from the present calculations are able to show the large efficiency of the state-changing channels involving rotational states of this cation. In fact, we find them to be similar in size and behavior to the inelastic and reaction rate coefficients obtained in previous studies, where H atoms were employed as projectiles. The same rotational excitation processes, occurring when free electrons are the collision partners of this cation, are also compared with the present findings. The relative importance of the reactive, proton-exchange channel and the purely inelastic channels is also analyzed and discussed. The rotational de-excitation processes are also investigated for the cooling kinetics of the present cation under cold trap conditions with He as the buffer gas. The implications of the present results for setting up more comprehensive numerical models to describe the chemical evolution networks in different environments are briefly discussed. � 2021 Author(s).