The collision-induced absorption (CIA) spectrum for nitrogen has been measured in the spectral region below 360 cm−1 at 126, 149, 179, and 212 K. The measurements have been obtained using Fourier transform infrared (FTIR) techniques, a far infrared (FIR) laser system operating at 84.2 and 15.1 cm−1, and microwave cavity techniques. The experimental line shapes have been compared with the theoretical predictions of Joslin, based on Mori theory, and of Joslin and Gray, based on information theory alone. The data have been used to determine the quadrupole moment employing various intermolecular potentials. One Lennard–Jones potential has resulted in a quadrupole moment of 1.51 B, the value that was used in generating the theoretical line shapes. These results, when combined with our forthcoming measurements on nitrogen mixed with methane and argon, may be helpful in determining the role of CIA in calculating the opacity of some planetary atmospheres.
The sideways displacement of an electromagnetic beam upon external reflection from a dielectric has been investigated. The experimental results, using 3 cm microwaves, are compared to those predicted by a theory based on a plane wave approach. The experiment has been completed for both perpendicular and parallel polarization as a function of total propagation distance at several angles of incidence around 45°.
The collision-induced spectra of mixtures of ethylene and each of the rare gases He, Ne, Ar, Kr, and Xe in the 40–360 cm−1 region has been obtained using a Michelson Fourier transform spectrometer. In addition, improved results for the collision-induced spectrum of pure ethylene gas are reported using this spectrometer as well as a far infrared laser source. All the results from the pure gas and gas mixtures have been analyzed according to the theory for quadrupolar-induced translation–rotational absorption. From this analysis the following values for the components of the quadrupolar tensor are: Qxx = −3.12, Qvy = 1.55, and Qzz = 1.57 B, which are somewhat lower estimates (in absolute value) than previously reported by us. Evidence for induction by other mechanisms (other than quadrupolar) has been obtained for the He–C2H4 and Ne–C2H4 mixtures.
The collision-induced absorption spectrum of a nitrogen-argon gas mixture is treated theoretically and the theory is applied to results obtained by us in the spectral region below 360cm-' at four temperatures, namely, 126, 149, 179, and 212 K. The measurements have involved the use of Fourier transform infrared and microwave techniques as well as a far-infrared laser system operating at 84.2 and 15.1 cm-I. The theoretical line shape is obtained from a convolution of a free rotation spectrum and a translational component. The spectra calculated from either information theory alone or combined with Mori theory both show good agreement with experimental results, especially above 30 cm-I. An important feature of the theoretical development is that no adjustable parameters need to be introduced.Le spectre d'absorption induite par collision d'un mClange gazeux azote-argon est CtudiC thkoriquement, et la thCorie est appliquCe aux rksultats que nous avons obtenus dans la rCgion spectrale situCe au-dessous de 360 cm-', pour quatre valeurs de la tempkrature, a savoir 126, 149, 179 et 212 K. Les mesures ont comport6 I'utilisation de TFIR et de techniques de micro-onde ainsi que d'un systkme laser fonctionnant dans I'infrarouge lointain, a 84,2 et 15,l cm-I. Le profil de raie thCorique est obtenu par convolution d'un spectre de rotation libre avec une composante translationnelle. Les spectres calcules, soit en utilisant seulement la thCorie de I'information, soit en en combinant celle-ci avec la thCorie de Mori, sont dans les deux cas en bon accord avec les rCsultats experimentaux, particulikrement au-dessous de 30 cm-I. Un aspect important du dCveloppement thkorique est qu'il ne requiert pas I'introduction de paramktres ajustables.[Traduit par le journal]Can. J. Phys. 64,7 (1986) 1. Introduction A recent theory (1, 2) of the collision-induced far-infrared absorption spectrum of nitrogen gas has yielded results that are in good agreement with the experimental data (3) over a wide range of temperatures. We have now extended the theory to a mixture of two dissimilar molecules, and as a test of the theory we have obtained results for a gaseous mixture of nitrogen and argon.In the theorv. it is assumed that the absomtion is due to the dipole inducedin the colliding molecules thrdugh a quadrupolar interaction and further that the gas is at a relatively low density such that the absorption is proportional to the product of the densities. By neglecting the small anisotropy of the nitrogenargon pair potential, we represent the spectral profile as the convolution of a free rotation spectrum with a translational component. Information theory is used to estimate the "leastbiased" form of the translational part based on a knowledge of spectral moments. The theory contains no adjustable parameters.The measurement of the far-infrared collision-induced absorption (CIA) spectrum of the nitrogen-argon mixtures required three different experimental techniques, as described earlier for the case of nitrogen. These included the use of a Fouri...
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