Accurate measurements of collision-induced absorption in CO2 are made at a number of temperatures in the range from − 40 to 60°C in the wavelength region 7–250 cm−1. Direct evidence for the separation of the pure translational band from the rotational–translational band is obtained at all temperatures. This and other aspects of the band shape are discussed. Over the entire temperature range, the experimentally determined Kramers–Kronig integral is found to be in good agreement with the theoretical value, i.e., the static dielectric constant. This agreement is achieved only when the contribution of the quadrupole–quadrupole energy in the radial distribution function, of particular importance for CO2 because of its large quadrupole moment, is calculated accurately. A value of the quadrupole moment is obtained, (4.5 ± 0.2)10−26 esu, which is in satisfactory agreement with that obtained by the method of Buckingham and Disch, which does not depend on a knowledge of intermolecular force constants. Induction due to higher multipole moments and the overlap interaction is considered.
The pure rotational spectr~lm of the tetrahedral n~olecule GeH4 has been studied with a 10.6 m lightpipe absorption cell and a conventional Michelson interferometer. Fifteen lines have been observed between 50 and 130 cm-I with a theoretical resolution of 0.5 cm-'. These lines have been identified as arising from forbidden ( J -> J + 1) transitions for the rotational levels J = 9-23. A detailed discussion is presented of the identification of the absorption n~echanisn~ with the distortion electric dipole moment pD produced in the ground vibronic state by centrif~~gal effects. Particular attention is paid to showing that the rotational transitions within the vibrational state v4 do not contribute to the observed spectrum. The theoretical problem of determining the rotational constant Bo and the scalar distortion constant D , from the data is considered. It is shown that the frequency shifts due to the fourth-rank tensor distortion interaction must be taken into account in the analysis. It has been determined that Bo = (2.696 f 0.003) cm-' and D , = (3.3 +_ 0.6) x lo-= cm-'. From estimates of absolute line intensities, it has been found that lpD1 -7.7 x D. -.---Le spectre rotationnel pur de la molCcule tetraedrique GeH, a Ct C etudik avec une cellule d'absorption a fibre o p t i q~~e de 10.6 m et un interferometre Michelson. Quinze raies ont etC observees entre 50 et 130cm-' avec uneresolution thCoriq~ede0.5cm-~. Ces raiesontete identifieesetattribueesades transitions interdites ( J -. J + 1) pour des nivea~lx rotationnels J = 9-23. On presente une discussion detaillee de I'identification du mecanisme d'absorption, avec le moment dipolaire Clectrique de distorsion pD produit a l'etat vibrationnel fondamental par effets centrifuges. Un soin particulier est pris pour demontrer que les transitions rotationnelles a I'intirieur du niveau vibrationnel v4 ne contribuent pas au spectre observe. Le probleme theorique de determiner la constante rotationnelle Bo et la constante de distorsion scalaire Ds a partir des donnees experimentales est considere. On montre que les decalages de frequence dus a I'interaction de distorsion tensorielle de quatrieme rang doit Ctre considere dans I'analyse. On a determine que B, = (2.696 + 0.003) cm-' et D, = (3.3 + 0.6) x cm-'. A partir d'evaluations d'intensit~s~absolues des raies, on a trouve que IpDI-7.7 x D. C'III. J I'hy\.. 51. IS82 (1973) [Traduit par le journal]
The far-infrared absorption spectrum of SF6 in the gaseous state was measured at 25°C at pressures from 3 to 19 atm in the wavelength region 12–250 cm−1. The absorption of liquid SF6 in this region was measured at 0°C and −40°C. The strongest bands in the gas phase are centered roughly at 50 cm−1, and approximately at 94 and 173 cm−1. Bands centered at approximately 55, 90, and 150 cm−1 were observed in the liquid phase. Since the intensity of the band at 50 cm−1 varies as density squared, it is ascribed to collision induction. The bands at 94 and 173 cm−1 in the gas phase (considered to be the same bands at 90 and 150 cm−1 in the liquid phase) vary linearly with density and are ascribed to the difference vibrations, respectively, ν4 − ν5 and ν5 − ν6. The hexadecapole moment of SF6 was estimated from the integrated intensity of the collision-induced band in the gas.
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