Two distinct rotational isomers of thioanisole-d(1) (C6H5S-CH2D) and thioanisole-d(2) (C6H5S-CHD2) with respect to the internal rotation of the methyl moiety have been identified and characterized spectroscopically using the resonantly enhanced two photon ionization, UV-UV hole burning, and slow-electron velocity map imaging techniques. From the statistical weights, the definite assignment for the specific rotational isomer of each isotopomer has been successfully done, providing isomer-specific ionization energies and vibrational frequencies of S-1/D-0 states. Detailed molecular structures, the methyl internal-rotor barrier, and normal-mode descriptions for selective vibrations are discussed with the aid of