Elastic collisions between Si and D atoms at low temperatures and accurate analytic potential energy function and molecular constants of the SiD(X²\Pi) radical

Interaction potential of the SiD(X^2\Pi) radical is constructed by using the CCSD(T) theory in combination with the largest correlation-consistent quintuple basis set augmented with the diffuse functions in the valence range. Using the interaction potential, the spectroscopic parameters are accurately determined. The present D_0, D_\rm e, R_\rm e, \omega _\rm e, \alpha _\rm e and B_\rm e values are of 3.0956 eV, 3.1863 eV, 0.15223 nm, 1472.894 cm^ - 1, 0.07799 cm^ - 1 and 3.8717 cm^ - 1, respectively, which are in excellent agreement with the measurements. A total of 26 vibrational states is predicted when J = 0 by solving the radial Schrödinger equation of nuclear motion. The complete vibrational levels, classical turning points, initial rotation and centrifugal distortion constants when J = 0 are reported for the first time, which are in good accord with the available experiments. The total and various partial-wave cross sections are calculated for the elastic collisions between Si and D atoms in their ground states at 1.0\times 10^ - 11--1.0\times 10^ - 3~a.u. when the two atoms approach each other along the SiD(X^2\Pi) potential energy curve. Four shape resonances are found in the total elastic cross sections, and their resonant energies are of 1.73\times 10^ - 5, 4.0\times 10^ - 5, 6.45\times 10^ - 5 and 5.5\times 10^ - 4 a.u., respectively. Each shape resonance in the total elastic cross sections is carefully investigated. The results show that the shape of the total elastic cross sections is mainly dominated by the s partial wave at very low temperatures. Because of the weakness of the shape resonances coming from the higher partial waves, most of them are passed into oblivion by the strong s partial-wave elastic cross sections.