Knowledge Bank

Spectral line positions and absorptivities for $H2O$, HDO, and $D2O$ lines in the far infrared at $0.06cm-1$ resolution from 10 to $400cm-1$ are presented, and the instrumentation used is described. The gases were diluted to 1 atm total pressure with $N2$ in a 20cm polyethylene-window cell. By use of spectral subtraction routines spectra of ``pure’’ $D2O$ and HDO were extracted from mixtures of $H2O,D2O$ and HDO. Spectra were converted to absorbance and absorptivities calculated and corrected for absorbance nonlinearity due to instrument resolution. The spectrometer used has been recently designed and built for high-senjsitiveitv hiehg-resolution vacuum-IR work. The rapid-scan interferometer designed with capillary sealed air bearings which allowed instrument pressures of less than 1 Torr to be maintained. It was also equipped with a liquid helium cooled germanium bolometer which increased system sensitivity two orders of magnitude over conventional systems equipped with a TGS detector.