Linewidth of the J = 12→32 Rotational Absorption in Nitric Oxide

The linewidths and intensities of the 10 lines around 150 GHz (5 cm−1) corresponding to the J = 12→32 transition in nitric oxide have been measured with a Fabry–Perot resonator. Collisions are the dominant broadening mechanism at the pressures of interest in this study (0.2–2 torr), although Doppler and saturation broadening are seen at lower pressures. The measured self-broadening linewidth parameter, averaged over the various lines, is 2.82 MHz/torr. This gives a nitric oxide collision diameter of 5.26 Å, which compares with 3.53 Å from kinetic theory. Line broadening due to a number of atomic and molecular species has also been measured. Collision diameters again exceed kinetic theory ones. This is attributed to dipole–dipole, dipole–quadrupole, quadrupole–quadrupole, and dipole–induced-dipole interactions.