Variable Temperature Pressure Broadening and Spectroscopic Studies Between 77 K and 600 K

Pressure-broadening coefficients are of both fundamental and practical importance. They are intimately connected with the intermolecular potential of collision dynamics and are necessary for many applications which involve the emission and propagation of electromagnetic radiation. The complexity of the problem however is such that for many fundamental species of molecules the pressure-broadening parameters of only a few transitions are known to better than 10%. In this thesis we report the results of the study of five molecular species of atmospheric interest broadened by foreign gas. Nitric acid (HNO_3) and NO_2 were studied at room temperature over a wide range of quantum states broadened by O ^2 and N_2. The results make possible a comparison of previous theoretical calculations on both molecules. In both cases we find a significant difference between the experimental data reported here and the earlier calculations using Anderson theory. A less extensive room temperature study on CF _2Cl_2, HOOH, and HDO was done. Comparison between the molecules of this study and those of the previous study on HNO _3 and NO_2 is considered. We have also developed a new cell for the study of the temperature dependence of pressure-broadening parameters. This cell employs the collisional cooling technique, which cools the sample gas against a cold background gas, and is usable down to 77 K. Using this new cell and an ordinary heated cell, several transitions of H_2O and HNO_3 broadened by O _2 and N_2 were studied as a function of temperature from 80 K to 600 K. In addition, we have used the collisional cooling technique to study the rotational and vibrational temperatures of molecules at 77 K. It is shown that the rotational temperature is equal to that of the buffer gas and that the vibrational temperature is determined by the temperature of the sample gas injector. Finally, the results of a spectroscopic study of the v_8 + v_9 vibrational band of HNO_3 will be presented. In this study, 107 transition frequencies have been measured and assigned from which the rotational constants can be determined.