ALBERT

Notizen: The microwave spectra of 12CF2(Double Bond)15N35Cl, 12CF2(Double Bond)15N37Cl, and 13CF2(Double Bond)14N35Cl have been recorded and analyzed. Rotational, quartic centrifugal distortion and quadrupole coupling constants were determined. The off-diagonal element of the chlorine quadrupole coupling tensor, χab, and the principal element of that tensor, χz, were obtained as 63.7 and −103.5 MHz, respectively, for 35Cl (average), and 51 and −82 MHz, respectively, for 37Cl in 12CF2(Double Bond)15N37Cl. During the analysis of the spectrum of the 13C species, it was necessary to diagonalize the complete exact Hamiltonian of the asymmetric rotor with two quadrupole nuclei because of irregular hyperfine patterns of some transitions caused by previously neglected matrix elements from the 14N quadrupole. Earlier data for the normal isotopic species were re-evaluated because neglected off-diagonal matrix elements of the Hamiltonian led to data for χab and χz inconsistent with the results obtained during this investigation. The rotational constants of all five isotopic species were used to determine the r0 structure. All structural parameters for the planar molecule except for the difference between the CF distances could be determined. The results for the distances r(C(Double Bond)N) and r(NCl) and the angle α(CNCl) were 1.254(27) Å, 1.713(17) Å, and 113.62(26)°, respectively. The experimental data for the structure, the inertial defect, and the centrifugal distortion constants are compared to results from ab initio calculations. © 1999 American Institute of Physics.

Notizen: The microwave spectra of the 13C-, 15N-, and 15N, D-substituted species of difluoromethanimine, CF2(Double Bond)NH, have been measured and assigned, and the rotational, centrifugal distortion, and quadrupole coupling constants have been determined. The ground state rotational constants of four isotopic molecules were sufficient to determine six independent parameters of the r0 structure. The difference between the C–F distances was indeterminate. The structure and the quartic centrifugal distortion constants are compared with the results from ab initio calculations with and without electron correlation. The r0 C(Double Bond)N double bond distance is 1.240(5) A(ring), halfway between the distance determined from single crystal x-ray diffraction and the ab initio distance (MP2/6-31G*). The molecular electric dipole moment forms an angle of about 8° with the direction of the N–H bond. © 1996 American Institute of Physics.

Notizen: 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 and chloride and of the liquid phases of propenoyl chloride and bromide have been used to obtain the enthalpy differences between the s-trans and s-cis conformers for these compounds. For the bromide and chloride the s-trans conformer is clearly the more stable form but the data are inconclusive for the fluoride. Complete equilibrium geometries have been determined for both rotamers of the fluorideand chloride by ab initio Hartree–Fock gradient calculations employing both 3-21G and 6-31G* basis sets. The structural parameters are compared to those suggested from microwave and/or electron diffraction studies of these molecules. Both calculations are consistent with the s-trans conformation being thermodynamically preferred for the fluoride molecule and the s-cis conformation for the chloride, which is contrary to the experimental data for the chloride. The 3-21G basis set was used to obtain the ab initio force constants and frequencies for the s-trans and s-cis conformers of both the fluoride and chloride with fixed scaling, variable scaling, and without scaling factors. These results required several reassignments of fundamentals for both conformers of both molecules. Improved vibrational data for both the fluoride and chloride were very valuable for the reassignments. These results are compared with the corresponding quantities for some similar molecules.

Notizen: The microwave spectrum of chloromethylphosphonic difluoride, ClCH2P(O)F2, has been investigated in the region from 26.5 to 39 GHz. The a-type R branch transitions have been assigned for both the 35Cl and 37Cl isotopic species for the trans conformer on the basis of the rigid rotor model. For the ground vibrational state the rotational constants for the 35Cl isotope were found to be A = 4392.4±2.3, B=1543.36±0.01, and C=1512.30±0.01 MHz and for the 37Cl isotope: A=4395.3±2.7, B=1502.04±0.01, and C=1472.54±0.01 MHz. With reasonably assumed structural parameters for the C–H and P=0 distances as well as the HCH angle, a diagnostic least-squares adjustment was utilized to obtain the other six structural parameters. The dipole moment components were determined from the Stark effect to be ||μa|| =2.28±0.05, ||μb|| =0.75±0.02, and ||μt|| =2.40±0.02 D. The infrared (3500–40 cm−1) and Raman (3500–20 cm−1) spectra of the gas and solid have been recorded. Additionally, the Raman spectrum of the liquid has been recorded and qualitative polarization values have been obtained. Boththe trans and gauche conformers have been identified in the vibrational spectrum of the fluid phases. From a temperature study of the Raman spectrum of the liquid phase the enthalpy differencebetween the trans and gauche conformers was determined to be 370±50 cm−1 (1.06 kcal/mol) with the trans conformer being thermodynamically preferred. Band contour simulation of the infrared gas phase bands also shows that the trans conformer is more stable in this phase. Upon crystallization only the trans conformer remains in the solid state. The asymmetric torsion for the trans conformer was observed as a series of closely spaced Q branches beginning at 82.5 cm−1 and falling to lower frequency and the corresponding transitions for the gauche conformer begin at 72.9 cm−1. These transitions have been used to obtain the potential constants for the asymmetric rotation. All of the normal modes have been assigned 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. All of these results are compared to similar quantities in some corresponding molecules.