Robin S. McDowell

Cw stimulated Raman gain spectroscopy of the ν1 fundamental of methane

Abstract We report near-Doppler-limited Raman spectra of the ν 1 fundamental in methane using direct cw stimulated Raman gain spectroscopy enhanced by a multipass optical cell. 25 MHz resolution makes possible a correct analysis of the fine structure of the ν 1 band of methane. We present line assignments to J = 10 and spectroscopic constants for this band which differ significantly from previous analyses.

Potential Constants of Iron Pentacarbonyl from Vibrational Spectra of Isotopic Species

The vibrational spectra of Fe(12C16O)5, Fe(13C16O)5, and Fe(12C18O)5 have been observed. Most of the fundamentals have been assigned, with some changes from earlier results in the literature. Potential constants have been calculated by constraining many of the interaction constants to values estimated from analogous constants of the hexacarbonyls. The results indicate that the axial CO bonds are stronger than the equatorial CO bonds. This implies that the axial MC bonds are weaker than the equatorial MC bonds, though the calculated MC potential constants are not significantly different.

Force constants of methane. Infrared spectra and thermodynamic functions of isotopic methanes

Abstract General quadratic valence force constants have been calculated for the symmetrical methanes ( CY 4 ) using the most recent experimental data. The F and G matrix elements are given for the isotopic species CY 3 Z and CY 2 Z 2 ( Y and Z are H, D, or T). The fundamental frequencies of CY 3 Z and CY 2 Z 2 were calculated using the CY 4 force constants. Most of the fundamental frequencies of these isotopic methanes were observed. The anharmonic corrections are discussed. From the force constants, zeta values were calculated for the degenerate vibrations of CY 3 Z . The thermodynamic quantities − (F 0 − E 0 0 ) T , (E 0 − E 0 0 ) T , S 0 , C p 0 , C p 0 , and equilibrium constants for the various H, D, and T isotope exchange equilibria are given at seven temperatures from −180°C to +1000°C.

Force Constants of Nickel Carbonyl from Vibrational Spectra of Isotopic Species

The infrared spectra of gaseous Ni(13CO)4 and Ni(C18O)4 and the infrared and Raman spectra of CCl4 solutions of these isotopic molecules were recorded. General quadratic valence force constants have been calculated from the frequencies of the normal species and the two isotopic species. The resulting force constant solution is similar to that obtained previously assuming a pi electron interaction potential function. These results put the force constants of metal carbonyls on a firmer basis.

Identification of the SF6 transitions pumped by a CO2 laser

Abstract The quantum numbers ( J values and octahedral symmetry types) of the SF 6 transitions from the ground state to v 3 = 1 that fall within ± 1.5 G Hz of the CO 2 P(14), P(18), and P(20) laser lines have been assigned. The SF 6 absorptions nearest these three laser frequencies are R(28) A 0 2 , P(33) A 1 2 , and an F 2 component of P(59) or P(60), respectively.

Electronic and vibronic states of uranium hexafluoride in the gas and in the solid phase at very low temperatures

Complex vibronic structure has been observed in the electric‐dipole‐forbidden charge transfer absorption bands of solid and matrix‐isolated UF6 in the temperature range 8–14 K. These bands have their maximum intensity near 260 and 375 nm. Associated with the 260 nm band are four electronic transitions with origins at 30 331, 31 032, 32 120, and 32 821 cm−1, the first two being observed directly. Two more no‐phonon transitions are associated with the weak band at 375 nm, one at 24 564 cm−1 and another at 25 265 cm−1. These levels are assigned via a weak j‐j coupling scheme as excitations from the ligand t1uσ orbital to empty uranium 5f orbitals. Uranium spin–orbit coupling in UF6 charge transfer states strongly resembles that of UF6 −. Several progressions in the symmetric stretch frequency ν1=580–595 cm−1 are present which have as their origins various combinations of the above electronic levels with the bending modes ν4, ν5, and ν6 or their overtones 2ν4, 2ν5, and 2ν6. Temperature effects, which account ...

The ν3 Q branch of SF6 at high resolution: Assignment of the levels pumped by P(16) of the CO2 laser☆

Abstract The Q branch of the ν 3 stretching fundamental of 32 SF 6 (ca. 947.6–948.3 cm −1 ) has been recorded at 109–142 K with a resolution of −4 cm −1 , and the individual transitions have been assigned. Several series of lines arising from different subbranches can be followed up to high J values ( J ≈ 80 in one case). Some of these subbranches form prominent band-heads that dominate the gross structure of the Q branch, especially at higher temperatures. A moderately strong transition at 947.742 cm −1 , displaced −8 MHz from the P (16) CO 2 laser line, has been assigned as Q(38) F 1 0 + E 0 + F 2 0 ; 39 other transitions that fall within ±300 MHz of the laser line have also been identified. The Q branch of 33 SF 6 , present in natural abundance (0.76%), has been recored and analyzed; the isotope shift is 8.97 cm −1 .

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.

Integrated infrared intensities and transition moments in SF6

The integrated infrared band intensities of the fundamental vibrational modes in SF6 have been measured by the Wilson–Wells–Penner–Weber method. The results are 1361±34 km mole−1 for the fundamental at 948 cm−1, and 74±2 km mole−1 for the fundamental at 615 cm−1. The transition moments derived from these measurements are 0.437±0.005 D for the 948 cm−1 fundamental and 0.126±0.002 D for the 615 cm−1 band. The transition moment was also derived from single line strengths in the 948 cm−1 band and found to be 0.42±0.03 D, in good agreement with the value found from band intensities.

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)