S. Kimel

Theory and Measurement of Pressure‐Induced Shifts of HCl Lines Due to Noble Gases

Pressure shifts of HCl absorption lines in both the 1–0 and 2–0 bands caused by five noble gases have been measured. An outstanding feature of these measurements is that the shifts are not the same for all lines of a band, but there is a strong dependence on the rotational quantum number J. However, there is evidence that the shifts tend to a constant limit for high J numbers. In order to interpret these results induction‐ and dispersion‐type van der Waals forces were considered and used in conjunction with existing line‐shape theories. In cases where perturbation theory can be applied, the limit shifts were accounted for fairly well, although no satisfactory explanation has emerged for the J dependence. Attention is drawn to the significance of observations of this sort as a means of obtaining information about intermolecular forces and molecular constants. Of particular interest is the possibility of obtaining such information for molecules in specific quantum states.

Infrared Spectra of HCl in Pure and Impure Noble‐Gas Matrices. Absolute Intensities

High‐resolution spectra were taken of the 1–0 absorption band of HCl trapped in argon, krypton, and xenon matrices in the temperature range between 6° and 50°K. The influence of impurities on such spectra was studied by introducing small quantities of a different noble gas into the matrices.A new spectral line, believed to be due to the combination of a ΔJ=0 transition with the constrained translational mode, is reported. Absolute intensities of the 1–0 band were measured and found to be 15 000, 18 500, and 18 000 darks in argon, krypton, and xenon, respectively. The spectra of HCl polymers are discussed.

Pressure Induced Shifts of HCl Absorption Lines in the Infrared

The shift of infrared absorption lines due to pressure changes are small and they are difficult to measure. However it has been found possible to study this effect with the large spectrometer in Rehovoth which is particularly suited for the determination of small wavelength differences. Pressure induced shifts of the individual lines of the HCl 2–0 band at 1.76 μ have been measured over a range of pressures below atmospheric. A strong dependence of the shift on the rotational quantum numbers was found. For self‐shifts the lines near the band center were shifted toward the blue and others toward the red. The results are discussed qualitatively. Measurements on shifts due to the addition of a foreign gas are also reported.

PRESSURE-INDUCED SHIFTS OF ABSORPTION LINES IN THE INFRARED

* Infrared absorption lines in addition to being broadened, are shifted as a result of increasing pressure of the sample. Studies of these pressure shifts provide information on intermolecular forces which is supplementary to that obtained from line widths. A technique has been developed of measuring shifts (~0.01 cm–1) due to pressure changes of about one atmosphere. Shifts of the individual lines of the HCl 2—0 band at 1.76 μ have been examined. In addition to HCl itself, polar and non-polar gases were used for pressurizing. A strong dependence of the shifts on the rotational quantum numbers was found. The “self” shifts were towards the blue for lines near the band centre and towards the red for lines distant from the centre.