Knowledge Bank

The frequency of the $(v2=1,J=1,K=0)\leftarrow (v2=0,J=0,K=0)$ infrared vibration-rotation transition of $N15H3$ coincides with that of the P(16) line of the $(001)\to (100)$ band of the $CO2$-laser (to within $0.1cm-1$). This absorption line is well isolated from other lines and is ideal for detailed laser spectroscopy. By using a 40 cm stable $CO2$-laser of single mode operation a strong absorption of the P(16) line has been observed while P(14), P(18) and P(20) lines are not much affected. From the pressure dependence of the absorption the frequency difference is estimated to be about 20 times as large as the pressure broadening parameter (method similar to Ref. 1). Measurement of foreign gas broadening and an attempt at double resonance is in progress. $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$T. Shimizu, Y. Ueda and K. Shimoda, Bull. Am. Phys. Soc. 14, 622 (1969).