The Raman (3200-lOcn_') and i.r. (3500-5Ocn-') spectra of methyl fluoroformate, CH,OC(O)F, and its deuterated analog, CD,OC(O)F, have been recorded in both the gaseous and solid phases. Additionally, the Raman spectra of the liquids have been recorded and depolarization ratios obtained. These data have been interpreted on the basis that the only stable conformation present at ambient temperature is the s-tram (methyl group trans to the fluorine atom). From far i.r. spectra of the vapor obtained at 0.1 cm -1 resolution, the methoxy torsional fundamental has been observed to shift from 182 to 168 cm-' upon deuteration of the methyl group. The methyl torsional fundamental has been observed in these spectra at 122 and 93 cm-' for the d, and d, compounds, respectively, and from these frequencies the barriers to internal rotation are calculated to be 369 cm-' (1055 cal/mol) and 356 cm-' (1018 cal/mol) for the CH, and CD, rotors, respectively. The structure, barriers to internal rotation and vibrational frequencies have also been determined from ab initio Hartree-Fock gradient calculations using both the 3-21G and 6-31G* basis sets. These results are compared to those obtained experimentally and to similar quantities for related molecules.