Microwave spectroscopy of HCOO13CH3 in the second methyl torsional excited state

Abstract The new experimental results and analysis of the microwave spectra of HCOO 13 CH 3 in the second methyl torsional excited state are reported. Pseudo-principal axis method (pseudo-PAM) was successfully applied to the normal methyl formate in the second torsional excited state and again applied to this isotopologue. We succeeded to assign 536 A-species transitions up to J  = 33 and K a  = 15 and 417 E-species transitions up to J  = 32 and K a  = 14. Thirty parameters were used to do the least-squares-analysis by using the pseudo-PAM Hamiltonian consisting of rotational, centrifugal distortion, and internal-rotational constants.