The two-dimensional anharmonic oscillator: The CCC bending mode of C3O2

Newly observed data on the rotational constants of carbon su?ide in excited vibrational states of the low-wavenumber bending vibration ν₇ have been successfully interpreted in terms of the two-dimensional anharmonic oscillator wavefunctions associated with this vibration. By combining these results with published infrared and Raman spectra the vibrational assignment has been extended and a refined bending potential for ν₇ has been derived: this has a minimum at a bending angle of about 24° at the central C atom, with an energy maximum at the linear configuration some 23 cm^?1 above the minimum. From similar data on the combination and hot bands of ν₇ with ν₄ (1587 cm^?1) and ν₂ (786 cm^?1) the effective ν₇ bending potential has also been determined in the one-quantum excited states of ν₄ and ν₂. The effective ν₇ potential shows significant changes from the ground vibrational state; the central hump in the ν₇ potential surface is increased to about 50 cm^?1 in the v₄ = 1 state, and decreased to about 1 cm^?1 in the v₂ = 1 state. In the light of these results vibrational assignments are suggested for most of the observed bands in the infrared and Raman spectra of C₃O₂.     

Doppler-limited spectroscopy of the 3ν3 band of SF6

The strongest portion of the 3ν₃ band of SF₆ has been recorded at T = 160 and 295 K with Doppler-limited resolution using a tunable laser difference-frequency spectrometer. The structure in this band has been identified with the P, Q, and R branches of one F_1u sublevel (with essentially l = 1 character) within the 3ν₃ vibrational manifold. Preliminary effective rotational constants have been obtained for this band from which the anharmonic parameters X₃₃, G₃₃, and T₃₃ can be estimated. The role of hot bands and of the other anharmonic sublevels is discussed in relation to prior interpretations of low resolution spectra and of the initial isotope selective stages of CO₂ laser photo-dissociation of SF₆.     

The infra-red spectra of silyl fluoride and silyl fluoride-d 3

Infra-red spectra have been recorded for silyl fluoride and silyl fluoride-d ₃ at a resolution of circa 0·3 cm^-1. Rotational structure has been observed for parallel fundamentals in both molecules, and for all perpendicular fundamentals. In both SiH₃F and SiD₃F the A ₁ and E species deformation modes interact strongly via a Coriolis perturbation; this has been analysed, and the band origin of v ₅ for SiH₃F is reassigned. A hybrid-orbital force field based on the experimental data is also reported.     

Chiral properties of tetrathiatriarylmethyl spin probes

We report that tetrathiatriarylmethyl (trityl) EPR probes are chiral molecules at room temperature, the two stereoisomers that differ in their helicity being configurationally stable enough to be separated and stored independently.     

Measurement and analysis of the ν2 and ν4 infrared bands of 13CD4

A Fourier transform infrared spectrum of 91% ¹³CD₄ has been recorded between 885 and 1193 cm^?1 with a resolution of 0.04 cm^?1. The frequencies of 600 lines were measured with an accuracy of ±0.003 cm^?1. Of these, approximately 368 are assigned as allowed transitions in ν₄, 95 are forbidden ν₄ transitions, and 137 belong to ν₂; maximum upper state J values are 20 for ν₄ and 19 for ν₂. The ground state tensor constants D_t, H_4t, and H_6t were obtained by fitting them to four rotational transitions observed by Kreiner and Opferkuch in the infrared-microwave double-resonance spectrum. An interacting-band analysis of the $\text{ν}{}_2\text{ν}{}_4$ diad then yields 22 spectroscopic constants for these Coriolis-coupled fundamentals and fits the experimental frequencies with an rms deviation of 0.0055 cm^?1 for 432 unblended lines that were assigned unit weight. A ν₄P⁺(12) transition at 943.3812 cm^?1, nearly coincident with the 10P(22) emission of the ¹²C¹⁶O₂ laser, has been investigated by heterodyne spectroscopy and its detuning (?64 MHz) and absorption coefficient have been determined. Such coincidences may lead to the development of laser analytical techniques for ¹³CD₄, which is a useful nonradioactive atmospheric tracer. ¹³CD₄ transitions that are within 300 MHz of isotopic CO₂ laser lines are tabulated for this purpose and for use in double-resonance experiments.     

High-resolution inverse Raman spectroscopy of the ν1 band of 28SiH4

A near-Doppler-limited isotropic Raman spectrum of the symmetric stretching fundamental ν₁ of ²⁸SiH₄ has been recorded between 2182.8 and 2187.0 cm^?1 using high-sensitivity “quasi-cw” inverse Raman spectroscopy. The band exhibits compact, nonoverlapping J manifolds, which were measured from Q(0) through Q(13), plus a portion of Q(14). Since ν₁ is in resonance with the nearby infrared-active stretch ν₃, these two bands were analyzed simultaneously using the infrared frequencies of ν₃ reported by Cabana, Gray, Robiette, and Pierre. The results confirm their analysis, in which several perturbation-allowed ν₁ transitions were identified in the infrared, but the molecular constants for the v₁ = 1 state are much better determined with the inclusion of the Raman data. At higher J, ν₁ exhibits significant intensity perturbations due to a breakdown of the selection rule ΔN = 0; these have been quantitatively accounted for.     

Intensity perturbations due to ν3/ν4 Coriolis interaction in methane

Formulas are obtained for the intensity asymmetry (Herman-Wallis) factors in the ν₃ and ν₄ fundamentals of methane due to the ζ₃₄ Coriolis interaction. The results are also applicable to the ν₃ and ν₄ bands of SF₆.     

Analysis of the ν1 and ν2 + ν4 bands of 12CH4

Line assignments, positions, strengths, and experimentally determined upper states are reported for the ν₁ and ν₂ + ν₄ infrared bands of ¹²CH₄. The bands have been analyzed using infrared spectra recorded with different optical densities and temperatures at 0.02- and 0.01-cm^?1 resolution using a four-passed grating spectrometer at Florida State University and a Fourier transform spectrometer at Kitt Peak National Observatory. Both ν₁ and ν₂ + ν₄ lines are assigned through J′ = 14. For J′ ≥ 10, the upper state of the vibrationally infrared inactive ν₁ band interacts strongly with ν₂ + ν₄ and is observed in the infrared spectrum with line strengths on the order of 10^?3 cm^?2 atm^?1. The upper-state energies and transition intensities are calculated from the molecular constants and transition moment matrix elements obtained through a simultaneous analysis of ν₁, ν₃, ν₂ + ν₄, 2ν₄, and 2ν₂.