Microwave spectra and centrifugal distortion constants of oxetane

The microwave spectra of oxetane (trimethylene oxide) and its three symmetrically deuterated isotopic species have been observed on a Hewlett-Packard microwave spectrometer from 26.5 to 40 GHz. For the parent species, the β-d2 and the αα′-d4 species, about 300 lines have been assigned for each molecule, and for the d6 species more than 600 lines have been assigned. The assignments range from v = 0 to v = 5 in the puckering vibration; although they are mostly Q transitions, either 3 or 4 R transitions have been observed for each vibrational state. The spectra have been interpreted using an effective rotational hamiltonian for each vibrational state, including five quartic distortion constants according to Watson's formulation, and a variable number of sextic distortion constants; in general, the lines are fitted to about ± 10 kHz. The distortion constants show an anomalous zig-zag dependence on the puckering vibrational quantum number, similar to that first observed for the rotational constants by Gwinn and coworkers. This is interpreted according to a simple modification of the standard theory of centrifugal distortion, involving the double minimum potential function in the puckering coordinate.

Excited vibrational state microwave spectra, structure, and force-field of trifluorosilane

The J = 2−1 microwave spectrum of six isotopic species of HSiF3 has been observed and assigned in excited states of five of the six fundamental vibrations. The assignment is based on relative intensities, double resonance experiments, and trial anharmonic force constant calculations. Analysis of the spectra leads to experimental values for five of the constants, all three l-doubling constants qt, one Fermi resonance constant φ233, and one zeta constant. The harmonic force field has been refined to all the available data on vibration wavenumbers, centrifugal distortion constants, and zeta constants. The cubic anharmonic force field has been refined to the data on and qt constants, using two models: a valence force model with two cubic force constants for SiH and SiF stretching, and a more sophisticated model. With the help of these calculations, the following equilibrium structure has been determined: re(SiH) = 1.4468(±5) Å, re(SiF) = 1.5624(±1) Å, HSiF = 110.64(±3)°,

Microwave spectrum of CF3CCH

Attempts to observe ΔK = ±1 transitions in the rotational spectrum of CF3CCH and CF3H in the first excited state of a degenerate vibration, by direct absorption in the Y band and K band regions of the microwave spectrum, have not been successful. In the course of this work the J = 3-2 and 4-3 rotational spectrum of CF3CCH has been observed with higher sensitivity than previously, and from the positions of the vibrational satellites several new rB values have been determined.

The microwave spectrum of thietan-2,2,4,4-d4

The microwave spectrum for thietan-2,2,4,4-d4 is analysed in six of its lowest puckering states and up to J = 25. The close lying pairs of states of vp = 0/1, 2/3 and 4/5 are treated with a vibration-rotation hamiltonian which includes an off-diagonal coupling term in vp. Additional corrections to this coupling term in higher powers of the angular momentum operator are derived and their importance for improving the fit of calculated to observed data is tested. The variation of the centrifugal distortion constants with vp follows the model of Creswell and Mills (1974, J. molec. Spectrosc., 52, 392). A value is determined for the derivative with respect to the puckering coordinate of the ac-component of the inverse moment of inertia tensor.

The microwave spectrum of 1-pyrazoline

The microwave spectrum of 1-pyrazoline has been observed from 18 to 40 GHz in the six lowest states of the ring-puckering vibration. It is an a-type spectrum of a near oblate asymmetric top. Each vibrational state has been fitted to a separate effective Hamiltonian, and the vibrational dependence of both the rotational constants and the quartic centrifugal distortion constants has been observed and analyzed. The v = 0 and 1 states have also been analyzed using a coupled Hamiltonian; this gives consistent results, with an improved fit to the high J data. The preferred choice of Durig et al. [J. Chem. Phys. 52, 6096 (1970)] for the ring-puckering potential is confirmed as essentially correct, but the A and B inertial axes are shown to be interchanged from those assumed by Durig et al. in their analysis of the mid-infrared spectrum.