The microwave spectrum,harmonic force field,and ground state average structure of 1,1-dichloroethylene

The microwave spectra of several isotopic species of 1,1-dichloroethylene have been measured up to high J values and have been analyzed for rotational constants and quartic centrifugal distortion constants. An approximate harmonic force field for the molecule has been obtained by combining the centrifugal distortion constants with known vibrational data. The harmonic force field has been used together with the results of the present and other microwave studies to determine the ground state average molecular structure.     

Centrifugal Distortion Analysis of a Near-Spherical Top, SO(2)F(2): The First Determination of All Six Quartic Centrifugal Distortion Constants for an Asymmetric Top

The rotational spectrum of the near-spherical top molecule SO(2)F(2) (sulfuryl fluoride) has been investigated by microwave Fourier transform spectroscopy and by millimeter-wave spectroscopy. The ground state spectrum has been measured from 10 to 472 GHz. One of the reasons for studying this molecule is that it is a nearly spherical top and we wanted to verify our theoretical prediction that for such a molecule all six quartic centrifugal distortion constants (and nine sextic distortion constants) should be determinable, while for a standard asymmetric rotor, Watson has shown that only five quartic and seven sextic distortion constants are determinable. The analysis of the spectra confirmed our predictions, because all six quartic constants were well determinable. The results have been confirmed independently by ab initio calculations of the force field and quartic distortion constants. Because the molecule is relatively heavy, contributions of some sextic constants are too small and we have not been able to determine all nine sextic constants predicted by theory. Copyright 2000 Academic Press.     

The pure rotational spectra of the lanthanum monohalides, LaF, LaCl, LaBr, LaI

Pure rotational spectra have been measured for all the major isotopomers of the lanthanum monohalides, LaF, LaCl, LaBr, and LaI, in their ground and (except for ) excited vibrational states. The spectra were observed with a cavity pulsed jet Fourier transform microwave spectrometer in the frequency range 5-24 GHz. The molecules were prepared by laser ablation of La metal and allowing the resulting plasma to react with SF₆, Cl₂, Br₂, or CH₃I precursor in an Ar carrier gas of the pulsed jet. For LaBr this is the first reported spectrum of any kind. Rotational constants, centrifugal distortion constants, nuclear quadrupole coupling constants, and nuclear spin-rotation constants have been determined for all the molecules. Accurate equilibrium (r_e) internuclear distances have given an indication of where the Born-Oppenheimer approximation is beginning to fail. From the centrifugal distortion constants and vibration-rotation (α_e) constants good estimates of the harmonic vibration frequencies and bond dissociation energies have been obtained. The halogen nuclear quadrupole coupling constants indicate the molecules to be highly ionic.     

The far-infrared rotational spectrum of nitrous acid (HONO) and its deuterated species (DONO) studied by high-resolution Fourier-transform spectroscopy

In this paper, we present the first high-resolution (0.003 cm⁻¹) absorption measurements of the pure rotational spectra of nitrous acid (trans- and cis-HONO) and its deuterated species (trans- and cis-DONO) in the far-infrared region between 40 and 150 cm⁻¹. The spectra were first assigned based on rotational constants from previous studies in the microwave and mid-infrared regions. New rotational and centrifugal distortion constants were determined for all four species. The accuracy of the principal rotational constants was improved, and several quartic and sextic (and even a few octic) centrifugal distortion constants were obtained for the first time. Synthetic spectra calculated using the new constants of this study reproduce the observed spectra very well.     

The microwave spectrum,harmonic force field,and structure of carbonyl chlorofluoride,OCCIF

Rotational spectra of three isotopic species of carbonyl chlorofluoride, OCCIF, have been extensively measured, and have been analyzed for rotational constants, quartic centrifugal distortion constants, and chlorine nuclear quadrupole coupling constants. Ab initio calculations of the harmonic force field have been made using several different sets of basis functions, and their relative cost efficiency has been assessed. The measured distortion constants have been combined with vibrational wavenumbers (both from the literature and from the present work) and with the ab initio force constants to refine the force field. Ground state effective (r₀) and average (r_z) structures have been evaluated for the molecule.     

Microwave spectra and centrifugal distortion constants of formic acid containing 13C and 18O: Refinement of the harmonic force field and the molecular structure

Pure rotational spectra of H¹³COOH, HC¹⁸OOH, and HCO¹⁸OH have been measured in the frequency region 8–185 GHz. Analysis of the spectra has given improved rotational constants and quartic and sextic centrifugal distortion constants. The quartic distortion constants have been combined with previously published distortion constants of four other isotopic species, and with the vibrational wavenumbers of seven isotopic species, to produce a refined harmonic force field. An improved substitution structure and the ground state average structure have been obtained. Some unmeasured transition frequencies which may be of importance in radioastronomy are also presented.     

The microwave spectrum, structure, chlorine nuclear quadrupole coupling constants, dipole moment, and centrifugal distortion constants of dichlorosilane

The microwave spectra of three isotopic species of dichlorosilane, SiH₂Cl₂, in its ground vibrational state, have been measured in the frequency region 8–40 GHz. The spectra have yielded values for the rotational constants, centrifugal distortion constants, and chlorine nuclear quadrupole coupling constants, as well as the molecular dipole moment, 1.13 ± 0.02 D. The molecule has C_2v symmetry, and the bond lengths and angles r(Si---Cl=2.033±Å, r(Si---H)=1.480±0.015Å, (Cl---Si---Cl)=109°43′±20±, (H---Si---H)=111°18′±40′ The centrifugal distortion constants have been compared with those calculated using a published force field.     

The harmonic force fields of methylene chloride and dichlorosilane from combined microwave and infrared data

The harmonic force fields of methylene chloride and dichlorosilane have been obtained by combining the vibrational wavenumbers and centrifugal distortion constants of several isotopic species. Although enough data were available from earlier work for dichlorosilane, it was first necessary for methylene chloride to determine its distortion constants from microwave spectra. Transitions were measured up to J = 80 and J = 90 for CH₂Cl₂ and CD₂Cl₂, respectively, and the analysis gave accurate rotational constants, and quartic and sextic distortion constants. Ground-state effective, substitution, ground-state average and approximate equilibrium structures have been obtained for both molecules.     

Millimeter and submillimeter wave rotational spectrum of pyridine in the ground and excited vibrational states

The pure rotational spectra of the ground and five excited vibrational states of pyridine were measured, assigned and fit in the 75-110 and 260-370 GHz frequency bands. An improved set of spectroscopic constants was obtained for the ground state, and all the rotational and quartic centrifugal distortion constants were obtained for the excited vibrational states.     

Ab initio calculations of phonon spectra in ATiO3 perovskite crystals (A = Ca,Sr, Ba,Ra, Cd,Zn, Mg,Ge, Sn,Pb)

First-principles calculations of phonon spectra based on the density functional theory are carried out for calcium, strontium, barium, radium, cadmium, zinc, magnesium, germanium, tin, and lead titanates with a perovskite structure. By analyzing unstable modes in the phonon spectrum, the possible types of lattice distortion are determined and the energies of the corresponding phases are calculated. From analyzing the phonon spectra, force constants, and eigenvectors of TO phonons, a conclusion is drawn concerning the nature of ferroelectric phenomena in the crystals studied. It is shown that the main factors determining the possible appearance of off-center atoms in the A position are the geometric size and electronic configuration of these atoms.     

The microwave spectrum of cyanophosphine, H2PCN

The rotational spectra of cyanophosphine, H₂PCN, have been measured between 10 and 42.5 GHz by Fourier transform microwave spectroscopy. The rotational constants, centrifugal distortion constants, the ¹⁴N quadrupole coupling constant, and the nuclear spin-rotation coupling constants of ³¹P have been determined. Density functional ab initio calculations were performed, and the calculated values of the molecular constants are in excellent agreement with our experimentally determined results. The spectra of three isotopomers were measured, H₂P¹²C¹⁴N, H₂P¹³C¹⁴N, and H₂P¹²C¹⁵N. The derived r₀ structure is quite comparable to the ab initio predicted H₂PCN equilibrium geometry.     

Submillimeter-Wave Spectroscopy of Phosphaalkynes: HCCCP, NCCP, HCP, and DCP

The submillimeter-wave rotational spectra of the unstable phosphorus-bearing molecules HCCCP (phosphabutadiyne) and NCCP (C-cyanophosphaethyne) have been investigated in selected frequency regions between 490 and 815 GHz using the Cologne Terahertz Spectrometer. Both molecules were studied in their ground vibrational states. Additionally, vibrational satellites within the bending states v(4) = 1 and v(5) = 1 were recorded for NCCP. Furthermore, the ground state rotational spectra of the (13)C and (15)N isotopomers of NCCP were detected in natural abundance. The new measurements allowed us to evaluate the sextic centrifugal distortion constants for each isotopomer and vibrational state investigated. The pyrolysis reactions, through which HCCCP and NCCP were produced in situ, also yielded phosphaethyne, HCP, as a by-product. Some transitions of HCP and DCP were recorded in their ground vibrational states along with v(2) = 1 vibrational satellites of the former. Copyright 2001 Academic Press.     

The microwave spectra of deuterated silanes,germanes, and stannanes

A previous measurement of the rotational spectra of SiH₃D, SiH₂D₂, and SiHD₃ has been extended in frequency region to determine rotational constants and quartic centrifugal distortion constants. Similar observations have been performed on GeH₃D, GeH₂D₂, and GeHD₃, consisting of five, three, and three Ge isotopes, respectively, and also on SnH₃D, SnH₂D₂, and SnHD₃ with seven, three, and three Sn isotopes, respectively. The observed rotational constants were analyzed to estimate the equilibrium internuclear distance for the three molecules.     

Millimeter-Wave Spectroscopy of Sulfur Dichloride

The rotational spectra of (32)S(35)Cl(2), (32)S(35)Cl(37)Cl, (32)S(37)Cl(2), and (34)S(35)Cl(2) in their ground vibrational states, as well as those of (32)S(35)Cl(2) and (32)S(35)Cl(37)Cl in their nu(2) and 2nu(2) excited states, have been studied in selected frequency regions between 100 and 370 GHz. Transitions involving a large range of quantum numbers have been observed, so that precise rotational and quartic centrifugal distortion constants could be determined for each of the spectra investigated. The complete set of sextic distortion constants was also obtained for the most abundant isotopomer in its ground vibrational state. The newly determined rotational constants of (34)S(35)Cl(2) and (32)S(37)Cl(2) allowed us to calculate the complete r(s) structure of sulfur dichloride using both single- and double-isotopic substitution methods. The quadratic force field has been refined using a larger set of quartic distortion constants and inertial defects. Copyright 2000 Academic Press.     

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.     

Sextic centrifugal distortion constants: interplay of density functional and basis set for accurate yet feasible computations

Quantum-chemical calculations assist the analysis of laboratory spectra, and often provide the only means to determine spectroscopic data that cannot be accessed experimentally. Accurate predictions of vibrational and rotational spectroscopic parameters are required for applications in the field of high-resolution molecular spectroscopy. While the accuracy issue of the quantum-chemical calculation of vibrational properties and of equilibrium structures has been addressed in the literature, the same is not true for centrifugal distortion constants that however play an essential role for the interpretation of remote sensing data. In this work, the performance of several model chemistries, rooted mainly in density functional theory, in computing sextic centrifugal distortion constants is assessed employing a benchmark set of molecules of both atmospheric and astrochemical relevance. The Jensen’s (aug-)pcs-n basis sets, different flavours of Dunning’s triple-ζ basis sets and the SNSD basis set, are employed in conjunction with different functionals, and their predictions are benchmarked against experimental and theoretical data at the coupled cluster level of theory. This study also demonstrates the reliability of the calculation of sextic centrifugal distortion constants within the Gaussian16 rev. B.01 program package. Reliable predictions of the sextic centrifugal distortion constants for the gauche- and trans-conformers of ethyl-mercaptan are also presented.     

The microwave spectrum of cyanophosphaacetylene, H2PCCCN

The a type transitions of the microwave rotational spectra of cyanophosphaacetylene, H₂PCCCN, have been investigated in the frequency region between 5 and 26.5 GHz by Fourier transformation microwave (FTMW) spectroscopy. Rotational, centrifugal distortion and ¹⁴N nuclear quadrupole coupling constants have been determined. Density functional theory level ab initio calculations were performed to predict the molecular constants, and the predicted values are in good agreement with our experimentally determined results. The ¹³C and ¹⁵N isotopomer transitions were also observed. The derived r₀ structure is quite comparable to the calculated H₂PCCCN equilibrium geometry.     

The harmonic force field and structure of chloryl fluoride

The microwave spectra of three isotopic species of chloryl fluoride, FClO₂, previously published by Parent and Gerry (J. Mol. Spectrosc., 49, 343–364 (1974)), have been refit to rotational constants and centrifugal distortion constants using Watson's Hamiltonian in both its A and S reductions. The quartic distortion constants have been combined with the vibrational data of Smith, Begun, and Fletcher (Spectrochim. Acta, 20, 1763–1770 (1964)) to calculate a refined harmonic force field. The rotational constants and force field have been used to calculate a zero-point average structure and an approximate equilibrium structure. Both the force field and structures are in essential agreement with those published earlier.     

Microwave spectra of the Cl and Cl isotopomers of dichloromethylene: Nuclear quadrupole-, spin-rotation-, and nuclear shielding constants from the hyperfine structures of rotational lines

The rotational spectra of the isotopomers C³⁵Cl³⁷Cl and C³⁷Cl₂ of dichloromethylene in the ground vibronic state were recorded in the range 10-33 GHz using a molecular beam Fourier transform microwave spectrometer. CCl₂ was generated by flash pyrolysis using different precursors. The observed spectra were analyzed to yield rotational and centrifugal distortion constants, as well as the complete Cl nuclear quadrupole coupling tensors and the spin-rotation interaction constants from the hyperfine structure of the rotational lines. With inclusion of data from previous work on the most abundant species C³⁵Cl₂ [N. Hansen, H. Mäder, F. Temps, Phys. Chem. Chem. Phys. (3) (2001) 50-55.] a refined r₀ structure was determined. The spin-rotation interaction constants of all three isotopomers were used to derive ³⁵Cl and ³⁷Cl principal inertial axis nuclear magnetic shielding components which have not yet been determined by NMR spectroscopy.     

The microwave spectrum and centrifugal distortion constants of difluoroborane,HBF2

The microwave spectra of two isotopic species of the unstable molecule difluoroborane have been measured between 8 and 36 GHz. Transitions have been measured up to J = 56 and K_a = 9 for H¹⁰BF₂, and up to J = 66 and K_a = 11 for H¹¹BF₂. Improved values for the rotational constants, boron nuclear quadrupole coupling constants, and quartic and sextic centrifugal distortion constants have been evaluated for both species.