Vibration-rotation Spectra of Formamides

Abstract Taking advantage of the Fourier transform infrared (FTIR) spectrophotometry in accumulating a very weak available radiation, which comes out from a multiple-reflection-type gas-cell (17 m), we have been able to record the infrared absorption spectrum of formamide (HCONH2 or DCONH2) at room temperature, where its vapor pressure is only 0.1 Torr (1 Torr≈133.322 Pa) in the order of magnitude. From an analysis of the rotational structure (resolution 0.5 cm−1) of the C–H stretching band, a revised set of parameters has been obtained. A Q-branch analysis was made for the v=2←0 and v=3←1 bands (resolution 0.24 cm−1) of the amino wagging vibration, where v is its vibrational quantum number. The rotational constants A−B were determined to be 2.0269 cm−1 for the v=2 state and 1.9990 cm−1 for the v=3 state, and the transition frequencies 657.75 cm−1 for v=2←0 and 769.85 cm−1 for v=3←1. On the basis of these new parameter values, a discussion was made of the amino wagging coordinate of this molecule.