Knowledge Bank

A Minimum-astigmatism multiple-reflection absorption cell, which matches the aperture of the NIST BOMEM Model DA3 FT spectrometer, has been designed and constructed The cell has a base length of 2 meters and is designed to be chemically inert. It can be used over pressures up to 12 atm and to temperatures down to $-45\circ C$, with optical path lengths up to 116 m. The optical system is substantially temperature independent. Conditions for minimum astigmatism will be discussed. This cell has been used to study the collision induced spectrum of the $v=1-0$ band of $N2$ gas around $2320cm-1$ at a path length of 84 m with pressure up to 12 aim at 6 temperatures over the range 228 to 296 K with a. resolution of $0.1cm-1$. Absorbance at any point in the hand is found to be proportional to the square of the gas density. The band profile is in good agreement with previous studies, but small features on the P-, Q- and R-branches, previously noted at much lower temperatures and attributed to dimeric $species1,2$, are also seen in our spectra. The total integrated absorption coefficient for the band is $3.467(6)\times 10\mathrm{<mrow\; data-mjx-texclass="ORD">-4</mrow>}$ $Amagar2$ at 293 K, and a. very small temperature dependence of this coefficient has been observed.