Global Analysis Of The Pure Rotational Spectrum Of Deuterated Methyl-formate

Organic molecules are closely related to the origin of life.As an important part of astrophysics,organic chemistry and biological research,it’s essential to study the structure and formation mechanism of organic molecules through spectroscopy analysis.This thesis studies the internal rotation of deuterated methyl formate(DCOOCH3)which is the isotopologue of methyl formate.Methyl formate is relatively abundant in interstellar medium.The large amplitude motion(or the internal rotation)of the methyl group splits each rotational line into a doublet(characterized by the symmetry labels A(σ = 0)and E(σ= ±1)).This thesis firstly describes some crucial theoretical issues in the assignment and analysis of the internal rotational spectrum of asymmetric-top molecules,such as effective Hamiltonian,selection rules,then compares two main effective Hamiltonian methods:principal axis method(PAM)and rho-axis method(RAM).Two kinds of RAM computer programs,BELGI and RAM36,are described in detail and used to assign and fit the rotational-torsional spectrum of DCOOCH3,respectively.We fit globally 31 spectroscopic constants of DCOOCH3 to 4466 transitions with highest values of J = 69 and Ka = 39 of the ground and first excited torsional states(vt=0 and 1)which combines previous measurements from the literatures with new measurements from JPL.