H. Flicker

Vibrational levels and anharmonicity in SF6—I. Vibrational band analysis

Abstract The vibrational spectrum of SF 6 has been recorded with a Fourier-transform i.r. spectrometer at a resolution of 0.05 cm −1 and pressure—path length products of up to 2 × 10 5 Torr-cm. Twenty-nine bands were observed. Rotational structure was resolved for 11 of these and polynomials were fitted to the observed frequencies to yield the scalar spectroscopic constants, including the band origins m and derived values of B′  B 0 and the Coriolis constants ζ. For 12 other unresolved bands accurate estimates of the origins could be made from the frequency of a sharp Q -branch edge. Three more bands (ν 3 , 2ν 1 + ν 3 , and 3ν 3 ) were not resolvable at our resolution but have been previously analyzed from Doppler-limited or sub-Doppler spectra. In addition, about 10 assignable hot bands were observed whose frequency shifts relative to the principal transitions could be accurately measured; two of these were sufficiently resolved for full scalar analyses. These frequencies were combined with results of several high-resolution Raman studies by other authors to yield the most complete data set on SF 6 vibrational levels yet obtained. Isotopic frequency shifts have also been measured. The effective Coriolis constants for combination and overtone bands of octahedral molecules are discussed.

Octahedral fine-structure splittings in ν3 of SF6☆

A report is made of high-resolution spectrum of ..nu../sub 3/ of SF/sub 6/ in which extensive portions of the rotational fine structure in the P and R branches are resolved for the first time. A preliminary analysis was made of this band, and rotational and octahedral splitting quantum numbers to the transitions were assigned. Similar spectra were obtained of the bending fundamental ..nu../sub 4/ at 615 cm/sup -1/.(auth)

Measurement and analysis of the infrared‐active stretching fundamental (ν3) of UF6

High‐resolution spectra of the infrared‐active stretching fundamental ν3 of 238UF6 have been obtained between 620.6 and 633.5 cm−1 using tunable semiconductor diode lasers. Interference from hot bands was suppressed by cooling the UF6 in a supersonic expansion, and useful monomer concentrations were produced with effective temperatures of <100 K. Portions of the band from P(77) to R(66) are illustrated. All transitions from the vibrational ground state have been assigned, and the Q branch has been fully analyzed. A total of 43 line frequencies and 110 frequency differences extending in J to P(77), Q(91), and R(67) has been used to fit seven spectroscopic constants. The ground‐ and excited‐state values of the rotational constant B could be individually determined, and the U–F bond length in the ground vibrational state is r0=1.9962±0.0007 A. The Q branch of 235UF6 has also been analyzed and the 235UF6–238UF6 ν3 isotope shift measured to be 0.603 79±0.000 17 cm−1. The isotope shift and the Coriolis constant...

High resolution spectroscopy of the OsO4 stretching fundamental at 961 cm−1

The ν3 bands of 187Os16O4, 189Os16O4, and 192Os16O4 have been recorded using both a Michelson interferometer (resolution 0.06 cm−1) and a tunable semiconductor diode laser (resolution limited by the Doppler width, ∼0.0007 cm−1). The rotational fine structure differs from that of most other spherical‐top molecules, for only rotational levels of A symmetry exist. A total of 112 individual vibration–rotation lines in the P and R branches of the three isotopic species were calibrated against stimulated emission lines from a high‐voltage CO2 gain cell, and were used to determine three scalar and two tensor spectroscopic constants for each species; an additional scalar constant was obtained from an analysis of the Q branch of 192OsO4. The strength of P (11) A2 0 was measured for 192OsO4 and yields a vibrational transition moment for ν3 of 0.17±0.02 D. Transitions of all isotopic species that are expected to fall near CO2 laser lines in the region 949–972 cm−1 are tabulated as an aid in the interpreation of satu...

High-resolution spectroscopy of the 16-μm bending fundamental of CF4

Abstract The 16-μm bending fundamentals ( ν 4 ) of 12 CF 4 , 13 CF 4 , and 14 CF 4 have been observed at Doppler-limited resolution using a tunable PbSnSe semiconductor diode laser. The tetrahedral splittings of the rotational manifolds have been observed in all three branches, and in particular the dense and partially overlapping transitions in the Q branches have been resolved and assigned. A least-squares fit of the Hamiltonian, including off-diagonal terms, yielded five scalar and three tensor spectroscopic constants for each of the three isotopes. From these constants the upper-state rotational constant B 4 and the Coriolis constant ζ 4 have been calculated, together with some of the other molecular constants. An absorption feature at about 0.18 cm −1 to the red of the main Q branch of each isotopic species has been identified as the Q branch of ( ν 2 + ν 4 ) − ν 2 , which is the transition that lases when CF 4 is pumped by a CO 2 laser at 9.4 μm (i.e., in ν 2 + ν 4 ).

High-resolution infrared spectrum and analysis of the ν9 band of ethane at 12.17 μm

Abstract The ν9 degenerate fundamental of C2H6 near 12.17 μm (822 cm−1) has been recorded at medium resolution (Δν = 0.125−0.500 cm−1) and high resolution (Δν = 0.04−0.05 cm−1) using both grating and interferometric spectrometers. The spectra have been assigned and analyzed by both standard and band contour techniques. The high-resolution spectrum showed a pronounced l-doubling in the K = 0 subband and the presence of a (2,2) type l-resonance. The assigned lines were corrected for these effects and analyzed using an energy expression through third order ( h 3 † ) with partial fourth-order ( h 4 † ) contributions. The standard deviation for the analysis of 549 of 569 assigned transitions was 6.7 × 10−3 cm−1. The ν9 band has been observed recently on Jupiter, Saturn, Titan, and Neptune by several workers. Spectra, frequency listings, and assignments have been included for use in future work on C2H6 in the atmospheres of the outer planets.

Analysis of 3ν3 in SF6

Studies of the 3ν3 absorption band in SF6 in the spectral region from 2800 to 2850 cm−1 have been completed with a FT–IR spectrometer at a spectral resolution of 0.04 cm−1. This study confirms the results reported earlier by Kildal on the general shape of this absorption band. The absorption has been studied as a function of temperature, allowing a definite assignment to be made of the ground state features observed in this spectrum at room temperature. The ground state absorption to 3ν3 appears with a double Q branch [estimated band origins at 2830.22 and 2827.62 (±0.06) cm−1]. The intensities and temperature dependence studies confirm the assignment by Fox of these two Q branches to the two F1u components of the 3ν3 state.

The ν 2 band of N 2 O as a frequency standard in the17-μm region of the infrared

Direct measurements of the absorption spectra of N/sub 2/O were made in order to determine if higher order terms are needed before the ..nu../sub 2/ band can serve as a frequency standard.(AIP)

Spectroscopy of 12 CF 4 features near the 9-μm 12 C 16 O 2 R(10), R(12), and R(18) lines by CO 2 -laser and diode-laser spectroscopy

The (12)CF(4) molecule has been made to lase at various wavelengths in the 16-microm v(4) + V(2) ? V(2) band by pumping in the 9-microm 0 ? V(2) + V(4) band with (12)C(16)O(2) lines. The strongest reported (12)CF(4) laser line occurs at 615.06 cm(-1) and is pumped by 9R12 [9-microm band, R(12) line]. We have measured, by two techniques, the absorption of (12)CF(4) in 9R12, and also in 9R10 and 9R18, which are known to result in weak 16-microm laser transitions. This was done both at room temperature and at an estimated 100 K, and striking changes in spectral features were noted as the temperature was lowered. For the 9R12 laser line, we find a (12)CF(4) feature located 30 +/- 3 MHz to the high-frequency side of line center, with a peak absorption coefficient of 5 x 10(-4) to 9 x 10(-4) cm(-1) Torr(-1), depending on temperature. By contrast, there are only weak (12)CF(4) features within +/-40 MHz of the 9R10 and 9R18 laser-line centers, and the absorption coefficients of those features are 1 x 10(-4) to 2 x 10(-4) cm(-1) Torr(-1).

High-resolution Q-branch spectra of the ν2 + ν7 bands of C3O2 in the 12 u̧m region

Tunable diode laser spectra are obtained of several Q branches in the ν2 + ν7 sum bands of 12C316O2 at 820–850 cm−1. Molecular constants are determined for the ground-state transition at 819.69 cm−1 and for the first two hot bands, which are shifted to higher frequency. The l-doubling constant in the ν71 state was found to be 4.16 ± 0.06 × 10−4 cm−1, and that in the ν2 + ν71 state 2.96 ± 0.04 × 10−4 cm−1.