Internal axis molecular parameters, torsional energies and matrix elements of methyl mercaptan-D1

In this paper an internal axis method Hamiltonian model has been applied to evaluate the torsional-rotational molecular parameters of asymmetrically substituted methyl mercaptan (CH2DSH) using previously observed microwave transitions. The torsional barrier potential barrier functions V1, V2 and V3 have been refined. The observed microwave transition frequencies have also been fitted to an energy expansion model, which allowed accurate predictions of yet unobserved transition frequencies with microwave accuracy. These values are independent of the Hamiltonian model used and will prove valuable for astrophysical detection. The matrix elements between various torsional sub-levels upto the fourth excited torsional state in the ground vibrational state.