VIBRATIONAL-SPECTRA IN THE CARBONYL STRETCHING REGION OF ISOTOPOMERS OF FORMAMIDE IN THE GASEOUS AND LIQUID STATES

IR spectra in the carbonyl stretching region of six isotopomers of for mamide (HCONH2, HCOND2, DCONH2, DCOND2, (HCONH2)-C-13, and (HCONH2)-N- 15) in the gaseous state at a temperature of 120 degrees C are present ed. From the frequency shifts observed it is concluded that the carbon yl stretching band is largely a stretching of the carbonyl group with only minor contributions from the CN stretching and CH bending vibrati ons. Calculations with a known force field confirm these results. Howe ver, some discrepancies between the observed and calculated frequencie s are observed. This is most likely due to a Fermi resonance in some o f the isotopomers. Changing the gas phase values of the CO and CN stre tching diagonal force constants only gives satisfactory agreement betw een the calculated frequencies and the observed frequencies in the liq uid state. Upon heating, the Raman carbonyl bands of neat liquid HCONH 2, neat liquid HCOND2, and an equimolar mixture of the two shift to di fferent extents. This is most likely due to differences in the carbony l stretching normal coordinate.