Browsing by Author "Lourderaj, U."

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    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.
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    Rotational state-changes in C5N? by collisions with He and H2
    (Oxford University Press, 2023-04-28T00:00:00) Biswas, R.; Giri, K.; Gonz�lez-S�nchez, L.; Gianturco, F.A.; Lourderaj, U.; Sathyamurthy, N.; Veselinova, A.; Yurtsever, E.; Wester, R.
    The anion C5N? is one of the largest linear (C, N)-bearing chains detected in the interstellar medium. Here we present and discuss the general features of new ab initio potential energy surfaces describing the interaction of this linear anion with He and H2. We employ a Legendre Polynomials expansion representation for the former and an artificial neural network fit for the latter. We then carry out quantum scattering calculations to yield rotationally inelastic cross-sections for collisions with He and H2, using relative translational energy values in the range of 0.1-300 cm?1. We then obtained the corresponding inelastic rate coefficients as a function of temperature covering the range from 1 to 100 K. The results for these two systems are compared with each other, as well as with the earlier results on the C3N? colliding with the same partners. We found that the final inelastic rate coefficients for this anion are all fairly large, those from collisions with H2 being the largest. The consequences of such findings on their non-equilibrium rotational populations in interstellar environments are discussed in our conclusions. � 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.