  Rate coefficient for state-to-state rotational transitions in H+ collision
with CS has been obtained using accurate quantum dynamical close-coupling
calculations to interpret microwave astronomical observations. Accurate three
dimensional ab initio potential energy surfaces have been computed for the
ground state and low-lying excited states of H+ - CS system using internally
contracted MRCI method and aug-cc-pVQZ basis sets. Rotational excitation and
deexcitation integral cross sections are computed at low and ultra low
collision energies, respectively. Resonances have been observed at very low
energies typically below 50 cm-1. Among all the transitions, Deltaj=+1 and
Deltaj=-1 are found to be predominant for excitation and deexcitation,
respectively. Deexcitation cross section in the ultracold region is found to
obey Wigner's threshold law. The magnitude of state-to-state excitation rate
obtained is maximum for j'=1 in the temperature range 2-240 K while minimum for
deexcitation in ultracold region. The rotational excitation cross-section
obtained using vibrationally averaged potential show rotational rainbow maximum
for j'=2 state. From simple unimolecular kinetics, the mean lifetime of
rotationally excited CS trap is estimated to be 550 ns due to the H+ collision
at microkelvin temperature enabling precise spectroscopic measurement and
studying molecular properties near quantum degeneracy.
