D. P. Eastman

Breadths and shifts of molecular band lines due to perturbation by foreign gases

Abstract The shifts in frequency and the half-intensity widths (HIW) due to foreign gases have been measured in the fundamental bands of HCl 35 , DCl 35 , and HBr 79 , and in the 1-0 and 2-0 bands of CO. The salient features of these effects are the linear dependence of shifts and widths upon the density of the foreign gas, the strong J dependence, and the dependence of the maximum shift observed upon the vibrational quantum number of the band and the polarizability of the foreign gas. The results are in agreement with similar earlier work.

Rotational and Vibrational Constants of the HCl 35 and DCl 35 Molecules

The 1–0, 2–0, 3–0, 4–0, and 5–0 bands of HCl35 and the 1–0 and 2–0 bands of DCl35 have been measured with high precision. A critical analysis has been made to determine the rotational and vibrational constants of these molecules. It is necessary to use a polynomial in m of the sixth degree to satisfactorily represent the frequencies of the band lines in the case of the most precisely measured bands. B0 for HCl35 has been found to have a value of 10.440254±0.000010 cm−1. B0 for DCl35 was found to be 5.392261±0.000010 cm−1. When the B0 obtained for DCl35 is combined with the microwave measurement of B0 by Cowan and Gordy the value obtained for the velocity of light c=299 793.1±0.65 km/sec. The observed rotational and vibrational constants (Ylj) have been used to calculate the potential constants of HCl35 by making use of Dunham’s theory of a rotating vibrator. It is shown that HCl35 is not a pure rotating vibrator since the observed and calculated values of Y02~De are in disagreement by about 1 part in 1000 which is approximately 10 times the experimental error. By making use of the molecular constants for HCl35 and DCl35 and the accurately known atomic masses it is deduced that the ground level Be is perturbed by the upper electronic levels by 1 part in 8000. The sign of the perturbation is to increase Be over its unperturbed value. The sign of the perturbation is such that it may be presumed the HCl molecule has a positive magnetic moment. It was calculated that μJ=+0.2 and +0.1 nuclear magnetons, respectively, for HCl35 and DCl35.

Highly Precise Wavelengths in the Infrared. II. HCN, N 2 O, and CO†

A discussion is given of the effect of mechanical errors in a grating drive on the accuracy with which line frequencies can be measured. It is shown that it is highly improbable that a mechanical device used to rotate a diffraction grating can be constructed with sufficient precision so that the line-frequency error will be determined by the optical information observable in the near infrared spectrum. By making use of the echelle spectrograph 67 lines of the 001–000 absorption band of HCN have been measured. Almost 400 lines from five N2O absorption bands arising from the ground state of the molecule have been measured. In addition, 11 lines from the 1–0 fundamental band of CO have been measured in order to determine ν0 for this band. In all cases only band lines have been measured which appear to be free of blends. The molecular constants of the above bands have been determined by making use of the combination relationships applying least-squares methods to the data. The line frequencies have then been calculated to four decimal places and presented in tables. The tables contain over 600 line frequencies. We believe the calculated line frequencies (lines free of blends) have an absolute accuracy of about 1 part in 5×106 and a relative accuracy referring to lines within a given band somewhat greater.

Vibration-Rotation Spectra of HCN†

An analysis of the spectrum of the linear unsymmetric molecule HC12N has been made permitting the determination of the 21 constants necessary for predicting the vibrational frequencies and the 10 constants necessary for predicting the B value for the various vibrational states. To determine these constants new measurements were made on numerous bands in the region of 1–3 μ employing a 5-m vacuum spectrograph. Several instances of Fermi resonance were detected and analyzed. Except for a few bands where additional resonances may be present, the vibrational constants predict the measured values for the band origins of 44 bands within an amount not much greater than the expected experimental error. The rotational constants also predict the B value within the experimental error for 24 bands where data are available.Bands of HC13N and DC12N were also measured to determine the α values for calculation of the equilibrium moment of inertia. The 101–000 and 1111–0110 bands were used for all three isotopic forms of HCN to determine the Be values in a parallel fashion. From these values the bond length C–H=1.06593±0.00010 A and C–N=1.15313±0.00002 A were determined.In five different cases in HC12N it was possible to apply the Ritz combination principle to determine the frequency of the 0110 state. By using this value and the rotational constants it was possible to calculate the frequencies of lines in the 0110–000 band. The principle is also applied to HC13N and DC12N.

Temperature Coefficient of Hypersonic Sound and Relaxation Parameters for Some Liquids

The spontaneous Brillouin effect has been used to determine the variation of sound speed with temperature in the temperature range of − 30° to + 160°C above the relaxation frequencies in dibromomethane, dichloromethane, and carbon disulfide, below any relaxation frequency of acetone and nitrobenzene, and in the region of dispersion in chloroform, carbon tetrachloride, benzene, and acetic acid. In some cases the speeds have been corrected for dispersion. The temperature coefficient of sound and the parameters that characterize the relaxation have been evaluated and compared with other determinations. The sound speeds as a function of temperature have also been measured in water and five viscous liquids; 1‐octanol, ethylene glycol, aniline, glycerol, and pentachlorobiphenyl. A simplified form of the Isakovich–Chaban theory involving a single temperature‐dependent relaxation time has been used to predict the dispersion in glycerol and pentachlorobiphenyl and the amplitude absorption coefficient in glycerol f...

Evidence for Structure in Plastics from Light Scattering

Measurements of the indices of refraction at 6328 A of polymerized methyl, ethyl, and butyl methacrylate (PMMA, PEMA, PBMA) as a function of temperature show a discontinuity in the slopes at the glass–rubber transition temperature. A similar discontinuity appears in the hypersonic speeds, obtained as a function of temperature from Brillouin shift measurements and the indices of refraction. From considerations involving the annealing process as seen in the index of refraction, the enhancement of the Rayleigh scattering, the large Landau–Placzek ratio, and the pronounced Krishnan effect (unequal depolarization of the horizontal and vertical components of 90° scattered light for horizontally polarized incident light), one concludes that the polymerization process freezes into the plastic shear and compressional strains that are only partially relieved by annealing.

Echelle-Type Spectrograph for the Near Infrared*

The 5-m evacuable double-passed grating spectrograph previously described has been modified so that all but 10 in. of the total optical path is now evacuable.The foreprism system has been redesigned so that overlapping high-order infrared spectra can be separated allowing the use of coarse gratings. Provision is made to keep the band pass of the foreprism monochromator in synchronization with the rotation of the grating.An addition to the scanning system provides wavelength markers on the recorder chart. The wavelength marker system is arranged so that accelerated scanning can be performed in traversing regions where lines are not being measured. The marker system is also useful in expediting the measurement of small frequency shifts.The procedure used for accurate determination of the dispersion by means of interferometric calibration is described.

Fine structure in the lines of the 2ν3 band of methane

Abstract The wavelengths of the lines of the 2 ν 3 band of methane have been remeasured under higher resolution than was formerly possible. Lines which were not resolvable by means of the grating alone but which were obviously complex were examined with a Fabry Perot etalon. The resolving power of the etalon was 400,000. By means of the line contours obtained with the interferometer it was possible to analyse many of the complex lines into their probable fine structures.

Stimulated Brillouin Effect in High-Pressure Gases*

Stimulated Brillouin scattering in gaseous nitrogen, methane, and carbon dioxide has been observed using a giant pulse laser and employing gas densities from 19 to 385 amagat. Stimulated Brillouin scattering was also observed in carbon-dioxide liquid at 26°C and through the transition temperature. The density threshold below which no Brillouin scattering was observed was 56 amagat for nitrogen, 19 amagat for methane, 350 amagat for gaseous carbon dioxide, and 385 amagat for liquid carbon dioxide. The velocity of sound in each case increases markedly with increasing pressure. The velocity of sound extrapolated to 1 amagat density for nitrogen and methane agrees closely with the isothermal velocity. There is some evidence to indicate an amplitude dependence on the measured velocities.

Precise Measurements of Some Infrared Bands of Hydrogen Chloride

Precision determinations of the origins of the fundamental and first four harmonic bands of HCl35 have been made. The rotational constants of the 2–0 and 3–0 bands as well as the origin and rotational constants of the 2–0 band of DCl35 are also reported. This work will be used in conjunction with additional measurements now in progress on the fundamental band of HCl and other bands of DCl to determine rotation-vibration constants for comparison with theoretical predictions.