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.     

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.     

The microwave spectrum,force field and dipole moment of CF2

Measurements of the microwave spectrum of CF₂ have been extended to include transitions up to J = 40. Using these extended measurements, a centrifugal distortion analysis has been performed and from the distortion constants, the force field, infrared spectrum, average structure, Coriolis coupling constants, and inertial defect have been calculated. The original assignment of the infrared spectrum has been confirmed. An improved value for the dipole moment, 0.469 ± 0.026 D, has been obtained.     

The microwave spectrum of the pyramidal isomer of disulfur difluoride: SSF2

The pyramidal isomer of disulfur difluoride, SSF₂, has been prepared by passing gaseous disulfur dichloride through heated potassium fluoride. The microwave spectra of three isotopic species of SSF₂ have been measured in the 26- to 76-GHz frequency region. For the most abundant isotopic species transitions with J values up to 79 have been observed. These data have been combined with previous measurements of low-J lines by R. L. Kuczkowski [J. Amer. Chem. Soc. 86, 3617–3621 (1964)] and fit to obtain values for the rotational constants and centrifugal distortion constants. The quartic centrifugal distortion constants have been used together with existing vibrational data to determine an harmonic force field for the molecule. Finally, ground state average and equilibrium structures have been calculated for SSF₂.     

Centrifugal distortion effects in SF2: Calculation of the force field and infrared spectrum

Measurements of the microwave spectrum of SF₂ have been extended up to J = 43 in order to account for the effects of centrifugal distortion. Seventy-five transitions have been included in a weighted least squares fit of the measured spectrum with an rms deviation of 0.078 MHz. The force field for SF₂ has been determined from the centrigufal distortion constants. The vibrational spectrum, as yet unobserved, has been predicted from the force field as have been the Coriolis coupling constants and the average structure.     

Molecular structure and harmonic force field of AsCl3 by microwave spectroscopy

The microwave spectrum of four isotopically substituted species of AsCl₃ in the frequency range 100–220 GHz has been investigated. Four r_s structures were determined resulting in the following average values of the bond length and bond angle:The harmonic force field of AsCl₃ has been calculated and compared with that obtained without the aid of the centrifugal distortion constants.     

The microwave spectrum,harmonic force field,and structure of formyl chloride

Extensive measurements were made of the microwave spectra of nine isotopic species of formyl chloride, HCOCl. Analysis of these spectra gave accurate rotational constants, chlorine nuclear quadrupole coupling constants, and centrifugal distortion constants. The distortion constants, together with the vibrational wavenumbers, were used to evaluate a valence harmonic force field. Effective, substitution, ground-state average, and estimated equilibrium structures are presented.     

Microwave spectrum and molecular force field of tetratomic C2v molecules: NO2Cl

The rotational constants and quartic centrifugal distortion constants for NO₂³⁵Cl and NO₂³⁷Cl have been determined from an analysis of rotational transitions in the microwave and millimeter wave regions between 8.2–40 and 90–120 GHz, respectively.The values of the in-plane force constants in the general harmonic potential field have been obtained by combination of infrared and microwave data. Vibrational frequencies of ¹⁴NO₂Cl and ¹⁵NO₂Cl, inertia defects of NO₂³⁵Cl in the excited vibrational states v₃ = 1 and v₅ = 1, and first-order centrifugal distortion constants of NO₂³⁷Cl are the experimental data used in the least-squares fitting determination of force constants.     

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.     

The microwave spectra of PH2D and PHD2, and the harmonic force field and structure of phosphine

Measurements of the pure rotational spectra of PH₂D and PHD₂ have been extended to include new Q-branch transitions and R-branch transitions. The rotational constants have been independently evaluated for the first time, along with some quartic and sextic centrifugal distortion constants. The spectrum of PD₃ has been reanalyzed to make the constants consistent with those reported for PH₃. The new results have been incorporated in a harmonic force field analysis. Both ground state average (r₂) and equilibrium (r_e) structures have been estimated.     

Comparison of empirical and ab initio force fields for phosphine

Existing experimental data on frequencies, Coriolis coupling constants, and centrifugal distortion constants for phosphine can be reconciled by means of a harmonic force field, provided substantial vibrational dependences of the distortion constants are permitted. Such dependences are indicated in a recent high-resolution study of PD₃. The resulting empirical force constants are then in excellent agreement with existing predicted values from a sophisticated ab initio study, including electron correlation.     

Rotational spectrum of ONCl in the (0, 0, 1) and (0, 1, 0) vibrational states and “b” type spectrum in the ground state. Comparison of force field obtained by different combinations of experimental data

From the rotational spectrum of ONCl in (0, 0, 1) and (0, 1, 0) excited vibrational states the inertia defects in these states have been determined. The “b” type rotational spectrum in the ground state has also been measured allowing the determination of Δ⁰ and of all the first-order centrifugal distortion constants.It is shown that by using differences of inertia defects Δ₂ and Δ₃ together with centrifugal distortion constants which do not involve the planarity relations and with harmonic vibrational frequencies of two isotopic species, the harmonic vibrational frequencies of two other isotopic species can be satisfactorily predicted.By using only inertia defects differences Δ₂ and Δ₃ as extra data, a definite choice can be made among the three sets of force constants which equally well reproduce the harmonic frequencies of four isotopic species.     

Vibration-rotation spectra and the harmonic force field of HOCl

Vibration-rotation spectra of HOCl have been measured at a resolution of 0.05 cm^?1 to determine vibration rotation constants, and 35–37 Cl isotope shifts in the vibration frequencies. The spectrum of DOCl has also been recorded, and a preliminary analysis for the band origins has been made. The vibrational frequency data and centrifugal distortion constants have been used to determine the harmonic force field in a least-squares refinement; the force field obtained also gives a good fit to data on the vibrational contributions to the inertial defect. The equilibrium rotational constants of HOCl have been obtained, and an equilibrium structure has been estimated.     

The microwave spectrum,harmonic force field,and structure of difluorodichloromethane

Very large numbers of rotational transitions have been accurately measured for ¹²CF₂³⁵Cl₂, ¹²CF₂³⁵Cl³⁷Cl, and ¹³CF₂³⁵Cl₂, and have been analyzed for rotational constants and quartic centrifugal distortion constants. The distortion constants have been combined with vibrational wavenumbers (both from the literature and from the present work), and with ab initio force constants also evaluated in the present work, to give an approximate harmonic force field. The rotational constants and force field have been used to evaluate ground state effective, substitution, and ground state average structures 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.     

Microwave spectrum of CHD2CN and CHD2NC,and the harmonic force field and rz structure of methyl cyanide and isocyanide

The microwave spectra of CHD₂CN and CHD₂NC have been measured from 18 to 40 GHz; about 20 type A and 30 type C transitions have been observed for each molecule. These have been fitted to a Hamiltonian using 3 rotational constants, and 5 quartic and 4 sextic distortion constants, in the I^rS reduction of Watson [in “Vibrational spectra and structure” Vol. 6 (1977)]; the standard error of the fit is 26 kHz. For methyl cyanide the 5 quartic distortion constants have been used to further refine the recent harmonic force field of Duncan et al. [J. Mol. Spectrosc.69, 123 (1978)], but the changes are small. Finally, for both molecules, the harmonic force field has been used to determine zero point average moments of inertia I_z from the ground state rotational constants for many isotopic species, and these have been used to determine an r_z structure. The results are compared with r_s structure calculations.     

The microwave spectrum of isotopically substituted hypochlorous acid: Determination of the molecular structure

Microwave spectra have been measured for four isotopically substituted species of hypochlorous acid (D¹⁶O³⁵Cl, D¹⁶O³⁷Cl, H¹⁸O³⁵Cl, H¹⁸O³⁷Cl). Both a- and b-type transitions have been analyzed for rotational, centrifugal distortion, and Cl nuclear quadrupole coupling constants. The distortion constants, together with vibrational wavenumbers, have been used to evaluate a valence harmonic force field. Effective, substitution, ground state average, and estimated equilibrium structures are presented.     

The harmonic force field and rz structure of HNCO

The presently available microwave, millimeter wave, and far-infrared data of five isotopic species of isocyanic acid, namely, HNCO, H¹⁵NCO, HN¹³CO, HNC¹⁸O, and DNCO, have been used to obtain improved values of the ground-state rotational constants, the five quartic distortion constants, and some higher-order distortion constants in the I^rS reduced Hamiltonian of Watson. The appropriate planarity relation among the quartic centrifugal distortion constants has been imposed in the fitting procedure. The general harmonic force field of isocyanic acid has been determined using all existing data, and assuming a trans bent equilibrium geometry of the molecule with an NCO angle of 170°. Finally an r_z structure has been obtained using the A_z, B_z, and C_z rotational constants of five isotopic species. The bending of the NCO chain is found to be 8° in the trans configuration.     

Microwave spectra of deuterated arsines: Distortion moment transitions of AsD3, microwave spectra of AsH2D and AsHD2, and the structure of arsine

Microwave spectra of three deuterated arsines have been measured and analysed. For AsD₃ distortion moment transitions have been observed for the first time, in the form of the K = ±1 ← ∓2 cluster; their frequencies have been combined with those of previously observed “normal” transitions to give rotational, centrifugal distortion, and ⁷⁵As hyperfine constants. For AsH₂D and AsHD₂, the measurements have been extended considerably and now include for the first time R-branch transitions; similar spectroscopic constants have been evaluated. The data have been combined with earlier results for AsH₃ and with vibrational data in a harmonic force field analysis. Both ground state average (r_z) and equilbbrium (r_e) structures have been estimated.     

The combined use of SCF-MO calculations and experimental data in the evaluation of quadratic force fields: MOCIC potential functions for fluoroform,methyl acetylene,and methyl cyanide

A semiempirical method combining SCF-MO calculations and limited vibrational data has been employed to evaluate the completely general quadratic potential fields of fluoroform, methyl acetylene, and acetonitrile. MOCIC (molecular orbital constraint using interaction coordinates) potential fields are presented for gas phase molecules of intermediate size. Here general harmonic force fields or excellent approximations utilizing extensive experimental data are available as standards. A statistical evaluation of the interaction potentials shows that there is some improvement in going from MNDO or ab initio SCF-MO force fields to the MOCIC functions which reliably reproduce the off-diagonal vibrational potential constants in most instances. The MOCIC primary compliants are excellent approximations of their vibrational counterparts, as expected. Comparison of the calculated isotopic frequencies, Coriolis coupling constants, and centrifugal distortion constants for the SCF-MO, MOCIC, and vibrational spectroscopic potential fields with the corresponding experimental values also shows MOCICs reliability for molecules with many interaction potentials. There is substantial improvement in the calculated isotopic frequency shifts and centrifugal distortion constants in going from SCF-MO to MOCIC functions.