Peter Groner

Analysis of torsional spectra of molecules with two internal C3v rotors. II. Far infrared and low frequency Raman spectra of dimethylether isotopes

The torsional far infrared and Raman spectra of gaseous CH3OCH3, CD3OCH3, and CD3OCD3 are presented. They are analyzed using a computer program which is based on the results of an extensive investigation of the isometric groups and of the symmetry groups of the rotation–internal rotation Hamiltonians of a series of semirigid two‐top models. Four or more Fourier coefficients of the potential functions in two variables could be determined for each isotope. Strong evidence was found for Fermi‐resonance‐type interactions with the COC bending mode.

Spectra and structure of organophosphorus compounds. XXIII. Microwave spectra, electric dipole moment, and molecular structure of two conformers of ethyldifluorophosphine

The microwave spectrum of ethyldifluorophosphine, CH3CH2PF2, has been investigated in the region from 18.0 to 39.5 GHz. The spectra of two conformers have been identified. The ground state and seven vibrationally excited states have been assigned for the more stable gauche conformer (phosphorus lone pair with respect to CH3 group), whereas the ground state and one excited state have been assigned for the trans form. Rotational and most quartic centrifugal distortion constants have been determined with A=6784.501(3), B=2930.156(2), C=2352.576(2) MHz for gauche and A=5444.910(3), B=3290.133(3), C=2871.915(3) MHz for trans, both in the ground state. Electric dipole moments were obtained from ground state Stark effect measurements: ‖ μa‖=1.990(4), ‖ μb‖=0.855(4), ‖ μc‖=0.091(7), ‖ μt‖=2.168(2) D for gauche and ‖ μa‖=1.780(10), ‖ μb‖=0, ‖ μc‖=1.077(10), ‖ μt‖=2.081(10) D for trans. Using a new computer program, a diagnostic least‐squares fit of the structural parameters suggests significant structural differen...

Effective rotational Hamiltonian for molecules with two periodic large-amplitude motions

Starting from a general Hamiltonian for a molecule with two periodic large-amplitude motions, an effective rotational Hamiltonian is developed for bound states of the internal motions. It contains two types of matrix elements: (i) The internal motion energy, expressed as two-dimensional Fourier series, and transformed to a reference axes system. (ii) Matrix elements of rotational operators in the reference axes system multiplied by two-dimensional Fourier series. The spectroscopic parameters are the coefficients of the Fourier series (integrals of localized functions), the internal motion parameters ρ, and the angles between the vectors ρ and the reference axes. Expressions are given for cases with higher symmetry. The effectiveness of the Hamiltonian is demonstrated by fitting the rotational spectrum of the ground state of dimethylether (356 frequencies involving levels up to J=25) to experimental precision. The data of five vibrational excited states can be fit to almost the same precision.

Vibrational spectra and assignments, normal coordinate analyses, abinitio calculations, and conformational stability of the propenoyl halides

The infrared and Raman (3500–30 cm−1) spectra of gaseous and solid propenoyl bromide, CH2 CHCBrO, have been recorded. The Raman spectrum of the liquid has been obtained and qualitative depolarization values have been measured. The fundamental asymmetric torsion for both the s‐trans and s‐cis conformers has been observed along with several hot transitions. From these transitions the potential function governing the internal rotation has been determined and the s‐trans to s‐cis barrier is 1861 cm−1 (5.32 kcal/mol), the trans conformer being more stable by 158±20 cm−1 (452±57 cal/mol). All normal modes have been assigned for the s‐trans conformer and many of those for the s‐cis conformer, based on band contours, depolarization values, and group frequencies. A normal coordinate calculation has been carried out by utilizing a modified valence force field to calculate the frequencies and the potential energy distribution for both conformers. Temperature studies of the Raman spectra of gaseous propenoyl fluoride...

Reinvestigation of the asymmetric torsional potential function in ethylphosphine

Abstract The far infrared spectrum of ehtylphosphine was measured at 0.12 cm −1 nominal resolution. These data were used together with splitting data from microwave spectroscopy to determine a new potential function for the asymmetric internal rotation which is in much better agreement with experimental data than the one published previously. The potential energy minimum for the gauche conformer is calculated to be 232 ± 10 cm −1 higher than the minimum of the trans form.

Analysis of torsional splittings in the microwave spectra of dimethylether, CH3OCH3 and its isotopes, CD3OCH3 and CD3OCD3

Abstract The multiplet splitting patterns of microwave transitions in the ground state and the first two torsional excited states of CH3OCH3, CD3OCD3, and CD3OCH3 were analyzed in terms of the semirigid rotor models C2vF-C3vT-C3vT and C 3 F- C 3v T- C 3v T . The following nonzero potential coefficients were obtained for CH3OCH3: V30 = V03 = 909.05 ± 0.49 cm−1, V′33 = 5.06 ± 1.60 cm−1; for CD3OCH3: V30(CD3) = 897.18 ± 2.41 cm−1, V03(CH3) = 910.45 ± 0.33 cm−1; for CD3OCD3: V30 = V03 = 897.00 cm−1. These results are compared to earlier microwave studies of these molecules.

Analysis of torsional spectra of molecules with two internal C3v rotors. XXIV. High resolution far infrared spectra of acetone‐d0, ‐d3, and ‐d6

The high resolution (0.10 cm−1) far infrared spectra of gaseous acetone‐d0, ‐d3, and ‐d6 were measured between 370 and 40 cm−1. The region of the methyl torsional transitions below 130 cm−1 was analyzed in terms of the semirigid rotor model for molecules with two internal C3v rotors and the two‐dimensional torsional potential functions were determined. Effective barriers of 291 cm−1 (832 cal/mol) and sine–sine interaction terms of −l08 cm−1 (−309 cal/mol) were found for all three isotopic species. The results are compared with those from ab initio calculations and from the analysis of splittings in the microwave spectrum.

Acetone: Laboratory Assignments and Predictions through 620 GHZ for the Vibrational-Torsional Ground State

The acetone molecule has a complex rotational spectrum arising from the internal rotation of two methyl tops and their interaction with each other and the rigid-body rotation of the molecule. Here we report the measurement and assignment of a large number of new rotational-torsional transitions of acetone in the vibrational-torsional ground state at frequencies of up to 620 GHz. The newly measured lines have been combined with previously measured transition frequencies and fitted by a procedure used successfully for dimethyl ether. From the fit to the global data set, we have extracted parameters that have enabled us to predict accurately the frequencies and intensities of over 10,000 lines of possible astronomical importance at frequencies of up to 620 GHz. The detection of interstellar acetone was first reported by Combes et al. based on two transitions with partially resolved internal rotation structure. The present work will aid further interstellar studies to verify acetone as an interstellar constituent.

Analysis of torsional spectra of molecules with two C3v internal rotors. IV. The torsional potential function for propane‐d0 and ‐d3

The Raman spectra of gaseous propane‐d0 and ‐d3 have been recorded between 50 and 3500 cm−1. Considerable torsional data are reported and used to characterize the torsional potential function based on a semirigid model. The average ’’effective’’ V3 for the propanes is found to be 1139±10 cm−1. The sine–sine coupling term is similar in magnitude but opposite in sign to the cosine–cosine coupling term in propane‐d0.

Spectra and structure of organophosphorus compounds. XXXIV. The rs and r0 structures of trans and gauche ethylphosphine

The microwave spectra of 11 chemically different isotopic species of ethylphosphine (CH3CH2PH2) including all 13C and D single substituted species were recorded and assigned for the vibrational ground state. The b‐ and c‐type transitions of the gauche conformers with symmetrically substituted ethyl groups and a PH2 group were found to be split due to tunneling between the equivalent forms. The spectra of these molecules were fit to a Hamiltonian containing Coriolis interaction terms. All other spectra were fit to asymmetric rotors with quartic centrifugal distortion. Complete rs structures were obtained for both the trans and gauche conformations. The r0 structures were derived from 45 and 48 rotational constants for the trans and gauche forms, respectively. Significant differences in the structures were found with the most notable one in the CCP angle which changes from 110.5° in the gauche form to 116° in the trans conformer. The methyl group in the gauche conformation is rotated away from a position sy...