Knowledge Bank

Spectra of the weakly-bound N$2$O-CO$2$, N$2$O-OCS, and N$2$O-N$2$ complexes in the region of the N$2$O $\nu 1$ fundamental band ($\sim$2224 cm$^{-1}$)areobservedinapulsedsupersonicslitjetexpansionprobedwithaquantumcascadelaser.Onenewbandisobservedforeachcomplex:twocombinationbandsinvolvingtheintermolecularin-planebendingforN$_2$O-CO$_2$ and N$2$O-N$2$ complexes, and the out-of-plane torsional vibration for N$2$O-OCS. The resulting intermolecular frequencies are 34.17, \textbf{138}, 044302 (2013).} 17.11 and 22.33 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ for N$2$O-CO$2$, N$2$O-OCS, and N$2$O-N$2$ complexes, respectively. The intermolecular vibrations provide clear spectroscopic data against which theory can be benchmarked. These results will be discussed, along with a brief introduction to our pulsed-jet supersonic apparatus which has been retrofitted by an infrared cw external-cavity quantum cascade laser (QCL) manufactured by Daylight Solutions. The QCL is used in the rapid-scan signal averaging mode. Although the repetition rate of the QCL is limited by its PZT scan rate, which is 100 Hz, we describe a simple technique to increase the effective repetition rate to 625 Hz. In addition, we have significantly reduced the long term frequency drift of the QCL by locking the laser frequency to the sides of a reference line.