Full-dimensional quantum scattering calculations of rovibrationally excited HD+HD collisions

Abstract

Full-dimensional quantum scattering calculations are reported for ro-vibrational transitions in HD+HD collisions using a highly accurate interaction potential for the H$_2$-H$_2$ system. Several near-resonant ro-vibrational transitions are identified that conserve the overall rotational angular momentum and nearly conserve the internal energy of the collision partners. Key anisotropic terms that drive the rotational transitions and angular momentum partial waves that contribute to low energy resonant features in the energy dependence of the cross sections are identified. The computed results are in agreement with total cross sections reported in previous experimental results, including resonant features in the energy dependence of the cross section. In particular, low-energy cross sections show a strong resonant feature associated with an $l=3$ partial wave in the incident channel. Rate coefficients for several inelastic rotational and ro-vibrational transitions are reported for temperatures ranging from $0.1$ K to $200$ K and they display a maximum between $1$ K-$10$ K reflecting the important contributions from the $l=3$ shape resonance that occurs around 2.5 K.

Figures (11)

• Figure 1: The leading expansion coefficients of the HD+HD interaction as functions of the intermolecular separation. Different terms are labeled by $\lambda_{1}, \lambda_{2}$, and $\lambda_{12}$ in that order. The inset provides an enlarged view of the leading terms in the region of the van der Waals potential well. Note that the bond lengths of both the HD molecules were fixed at 1.44 $a_{0}$.
• Figure 2: Elastic cross sections for ortho-H$_2$+ortho-H$_2$ collisions as functions of the collision energy computed using the ZCYBG, JPS, and Hinde PESs for the initial state $v_{1},j_{1},v_{2},j_{2}=0,1,0,1$.
• Figure 3: Integral cross sections as a function of the relative velocity from our calculations (red curves) and experimental data of Johnson et al. (black dots and circles). Experimental results johnson1979total are scaled by a factor of 1.8 to enable the comparison. A partial-wave analysis of the resonance features in the cross section is also presented. The dashed gray line is the velocity corresponding to the energy of the bound state supported by the $l=3$ effective potential computed by the LEVEL code le2017level.
• Figure 4: Diagonal terms of the effective coupling potential as a function of the intermolecular separation $R$ for the $v_{1} j_{1} v_{2} j_{2}=0000$ initial state. The different curves represent different partial waves, $l=0-5$. The dashed red line displays the energy of the $l=3$ resonance at 2.54 K computed using the LEVEL code le2017level.
• Figure 5: Integral cross sections for elastic and inelastic rovibrational transitions from initial state $v_{1} j_{1} v_{2} j_{2}=0110$ as functions of the collision energy. Different transitions are labeled by the text inside the figure along with the energy gap. Contributions from the even and odd exchange symmetries are indicated by dotted and dashed curves while their weighted sum is depicted by the solid curves for each transitions.