Speaker
Description
Tritium bearing hydrogen molecules are of a significant scientific interest, see Ref. [1] and, for instance, Tritium Laboratory Karlsruhe (TLK) reports at Karlsruhe Institute of Technology (Germany). In this work a quantum-mechanical close-coupling calculation is performed for elastic and inelastic 4-atomic collisions:
$ {\rm HT}(j_1)+{\rm HT}(j_2) \rightarrow {\rm HT}(j^{\prime}_1)+{\rm HT}(j^{\prime}_2)$ and ${\rm DT}(j_1)+{\rm DT}(j_2) \rightarrow {\rm DT}(j^{\prime}_1)+{\rm DT}(j^{\prime}_2)$. Here H is a hydrogen atom, D is deuterium, and T is tritium. Global six-dimensional symmetrical H$_2$-H$_2$ potential energy surfaces (PESs) [2,3] have been adopted and appropriately modified for current 4-atomic systems. Specifically, we changed the position of the center of mass in HT and DT. In this presentation a special attention will be given to different geometrical modifications of the multidimensional H$_2$-H$_2$ potentials, as in Ref.[4]. State-resolved integral cross sections $\sigma_{j_1j_2\rightarrow j_1'j_2'} (\varepsilon_{kin})$ for quantum-mechanical rotational transitions $j_1j_2\rightarrow j_1'j_2'$ in HT and DT molecules and corresponding state-resolved thermal rate coefficients $k_{j_1j_2\rightarrow j'_1j'_2}(T)$ have been computed. The relationship between the rate coefficient $k_{j_1j_2\rightarrow j'_1j'_2}(T)$ and the cross section $\sigma_{j_1j_2\rightarrow j'_1j'_2}(\varepsilon)$ can be obtained through the following weighted average: $k_{j_1j_2\rightarrow j'_1j'_2}(T)= \sqrt{\frac{8k_BT}{\pi\mu}}\frac{1}{(k_BT)^2}\int_{\varepsilon_s}^{\infty}
e^{-\varepsilon/k_BT} \times \sigma_{j_1j_2\rightarrow j'_1j'_2}(\varepsilon)\varepsilon d\varepsilon$, where $k_B$ is Boltzmann constant, $\mu$ is reduced mass of the molecule-molecule system and $\varepsilon_s$ is the minimum kinetic energy for the levels $j_1$ and $j_2$ to become accessible. Additionally, for comparison purposes, H$_2$+H$_2$/HD calculations for a few selected rotational transitions have also been performed. These energy transfer collisions are of fundamental importance in astrophysics, see for example Refs.[5-7], papers [4] and Ref. [8]. The hydrogen molecules HT and DT are treated as rigid rotors in our calculations. A pronounced isotope effect is identified in the title collisions.
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5. Balakrishnan N, Croft J F E, Yang B H, Forrey R C, Stanci P C, ApJ 866:95 (2018).
6. Wan Y, Balakrishnan N, Yang B H, Forrey R C, Stancil P C, MNRAS 488, 381 (2019).
7. Wan Yier, PhD Dissertation 2019, The University of Georgia, Athens, Georgia:
http://getd.libs.uga.edu/pdfs/wan_yier_201908_phd.pdf.
8. Sultanov R A and Guster D, Chem. Phys. Lett. 436, 19 (2007).
