Knowledge Bank

While there have been a number of recent studies of room-temperature $N2$-broadening of spectral lines in various molecular bands of HCN, the corresponding pressure-induced line shifts have not been measured. Only three limited studies of the temperature-dependence of $N2$-broadening in HCN have been reported, and air- and $O2$-broadening have been examined only at room temperature for single $HC15N$ rotational $line.a$ We have recorded over 80 new infrared spectra of HCN broadened by $N2,O2$, or air at room temperature and low temperatures using a 50-cm coolable cell with the McMath-Pierce Fourier transform spectrometer (FTS) of the National Solar Observatory on Kitt Peak, Arizona. Most of these spectra cover bandpasses of either $2750-3950cm-1$ at $0.008cm-1$ resolution or $600-3000cm-1$ at $0.005cm-1$ resolution. Volume mixing ratios of HCN in the broadening gases were 0.1% or less, and total sample pressures ranged from 12 Torr to over 500 Torr. Most spectra were recorded at temperatures from room temperature down to near the freezing point of HCN $(-13\circ C)$, and some spectra were successfully recorded at temperatures down to about $-60\circ C$. Several spectra of low pressures (about 0.1 Torr) of purified HCN were also recorded to provide line positions unaffected by pressure-induced shifts. An initial group of 19 of these absorption spectra have been analyzed simultaneously using our multispectrum nonlinear least-squares $techniqueb$ to determine $N2$-broadening and shift coefficients and their temperature dependences for transitions up to $J\prime \prime =30$ in the $\nu 1$ fundamental band of $H12C14N$. The results for $N2$-broadening compare well with available values reported in the literature. In particular, the $N2$-broadening temperature-dependence exponent n shows a quantum-number dependence similar to that observed in the $\nu 2$ band by Schmidt $etal.c$ Analysis of air-broadening and shifts in the $\nu 1$ band is in progress, as well as work on the $\nu 2$ and $2\nu 2$ band systems.