HIGH RESOLUTION INFRARED SPECTROSCOPY OF NO USING TUNABLE PbSSe LASERS

This work was sponsored by the Department of the Air Force.Author Institution: Lincoln Laboratory, Massachusetts Institute of TechnologyA detailed high resolution $(\leq 3\times 10^{-5} cm^{-1})$ study of indivudual absorption lines in the fundamental vibration-rotation band of NO has been made using tunable PbSSe semiconductor lasers operating near $5.3 \mu$m. These absorption spectra reveal previously unresolved fine structure in the R and Q branches due to A doubling, nuclear hyperfine splitting and Zeeman splitting. Experiments were performed at low pressure $(\leq 1 Torr)$ using small gas cells (4-10 cm) with magnetic fields up to 50 kG. Absorption spectra were obtained by sweeping the frequency of the laser through the absorption lines while measuring the cell transmission. The R(15/2)$_{1/2}$ absorption shows the Doppler profile at 0.2T with two A doubled components separated by 318 MHz. Each of these components splits into two apparent absorption lines in a magnetic field along the propagation direction. The measured splitting $(g = 0.028)$ is in excellent agreement with the calculated values using parameters deduced from microwave experiments. The R(15/2)$_{3/2}$ absorption appears as a single line due to the smallness of the A type spllitting (29MHz) relative to the Doppler width (127 MHz). This line splits into 14 major components in a longitudinal magnetic field with splittings in good agreement with the calculated values. Numerous absorption lines near the heads of the $Q_{1/2}$ and $Q_{3/2}$ branches have been studied. Nuclear hyperfine splitting as well as A doubling have been observed in the Q(1/2)$_{1/2}$, Q(3/2)$_{1/2}$ and Q(5/2)$_{1/2}$ lines and compared with the calculated lineshape. Excellent agreement is obtained with calculations using nuclear hyperfine coupling parameters deduced from microwave measurements