Knowledge Bank

Self-, $N2-,O2-,H2-,Ar-$ and He-broadening coefficients, pressure shifts and integrated intensities have been measured for R- and Q-branch transitions in the $\nu 1$ fundamental band of ammonia using a difference-frequency laser spectrometer. The J-K dependence of the broadening coefficients is very pronounced for self broadening, but much weaker for foreign gas broadening. Semiclassical line broadening calculations reproduce this rotational dependence for self broadening, but exaggerate it for $N2$ broadening. Comparison with earlier measurements on other bands of ammonia indicates very little vibrational dependence except for self broadening in the $\nu 2$ hot bands and $H2$ broadening in the ground state. Dicke narrowing is evident at intermediate pressures, yielding an average narrowing coefficient and an optical diffusion constant for each gas mixture. A small amount of line mixing is evident in the self-broadened Q-branch at pressures sufficient to overlap the inversion tunneling doublets.