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.     

Doppler-limited dye laser excitation spectroscopy of HCCl

The cw dye laser excitation spectrum of the $\text{A}\text{?}{}^1\text{A″(050) ←}\text{X}\text{?}{}^1\text{A′(000)}$ vibronic band of HCCl was observed between 16 539 and 16 656 cm^?1 with the Doppler-limited resolution, 0.03 cm^?1. The HCCl molecule was generated by the reaction of discharged CF₄ with CH₃Cl. The observed spectra were assigned to c-type transitions with ΔK_a = ±1 and also to axis-switching transitions with ΔK_a = 0 or ?2, but all with K′_a = 0, both for HC³⁵Cl and HC³⁷Cl. A rotational analysis yielded the rotational constants and quartic centrifugal distortion constants for the ground vibronic state and the band origin. A weak vibronic band, about one-third as intense as the main band, was found at about 57 cm^?1 to the violet of the main band for both isotopic species, and was ascribed to a transition from the ground vibronic state to a vibrational level, possibly (041), of the à state. The rotational levels of HC³⁵Cl in the à state showed a large perturbation; the J′ = 8, 9, and 10 levels were found to be split into two components. A normal coordinate analysis was carried out to calculate the centrifugal distortion constants and the inertia defect, which were in fair agreement with the observed values. The molecular structure of HCCl in the ground vibronic state was recalculated from the rotational constants of the two isotopic species combined with the 0.75B₀ + 0.25C₀ value previously reported for DC³⁵Cl.     

The microwave spectrum and centrifugal distortion constants of vinyl fluoride

The rotational spectrum of vinyl fluoride up to J = 40 has been assigned and measured in the frequency region 8–37 GHz. Both a- and b-type transitions were observed. These measurements have been combined with those made in other frequency regions to calculate refined rotational constants and to obtain all quartic and some sextic centrifugal distortion constants. A comparison is made between the quartic centrifugal distortion constants measured here and those calculated from vibrational data.     

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.     

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.     

Equilibrium structure and force field of nitrosyl chloride

The a-type rotational spectra of ¹⁶O¹⁵N³⁵Cl in the (100) excited vibrational state ($\text{ν}{}_1\text{? 1770}\text{cm}{}^{\mathrm{?1}}$) and of ¹⁸O¹⁵N³⁵Cl and ¹⁸O¹⁴N³⁷Cl in the ground state were observed. The equilibrium structure of nitrosyl chloride was calculated from the values of the equilibrium rotational constants B_e and C_e of the two isotopic species ¹⁶O¹⁴N³⁵Cl and ¹⁶O¹⁵N³⁵Cl. The ground-state rotational constants of seven isotopic species of nitrosyl chloride were used to calculate Watson's r_m structure, which was found to be in satisfactory agreement with the r_e structure. The quadratic and cubic force fields of nitrosyl chloride were simultaneously refined by optimizing the least-squares fit to a set of 48 experimental data which includes the sextic centrifugal distortion constants, with one quadratic and three cubic terms of the potential energy function constrained to the values computed by SCF/ab initio methods. All remaining quadratic and cubic SCF force constants were found to be in reasonably close agreement with the empirically determined constants.     

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 rotational a-type sepctra of 15N-labeled diazirine,H2CN2

The rotational a-type spectra of isotopically enriched diazirine isotopomers, H₂¹²C¹⁴N¹⁵N and H₂¹²C¹⁵N₂, have been recorded in the region between 8 and 300 GHZ; the latter isotopomer has been observed for the first time. Using Watson's A-reduced Hamiltonian, the rotational constants and the quartic and some sextic centrifugal distortion constants have been determined for the ground vibrational states.     

用从头算方法研究GeCl2分子的非谐振力场和光谱常数

用从头算方法的MP2和CCSD（T）方法结合cc-pVTZ基组计算了二氯化锗同位素（⁷⁰GeCl₂、⁷²GeCl₂和⁷⁶GeCl₂）分子的平衡结构、光谱常数和非谐振力场.二氯化锗的几何结构、转动常数、振转相互作用常数、谐频、非谐振常数、四次和六次离心畸变常数、三次和四次力常数的计算结果与实验结果符合较好,二氯化锗分子的同位素效应较小,可能的原因是Ge同位素的质量变化相对较小.两种方法计算的结果均与实验结果符合,但CCSD（T）方法比MP2计算结果的偏差稍大一些,可能的原因是CCSD（T）方法在描述过共价Cl原子的电子相关时不够充分.     

Centrifugal distortion analysis of difluoramine

The microwave rotational spectrum of difluoramine (NF₂H) has been analyzed in the frequency region 15–36 GHz involving rotational levels up to J = 19. The analysis gives refined rotational constants and all quartic centrifugal distortion constants. These constants have been used to predict additional Q-branch transitions of the molecule in the frequency region 5–95 GHz.     

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.     

The microwave spectrum of CHD2Cl

The ground vibrational state microwave spectrum of CHD₂Cl has been studied in the region 26.5–40.0 GHz. From the observation of weak c-type transitions the A₀ rotational constants of CHD₂³⁵Cl and CHD₂³⁷Cl have been determined to be 95 426.08 ± 0.06 and 95 425.23 ± 0.11 MHz, respectively. The observed a-type and c-type transitions have been used to obtain A, B, C, all five quartic and one sextic distortion constants present in the reduced Hamiltonian of Watson for the ³⁵Cl and ³⁷Cl isotopic modifications of CHD₂Cl.     

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,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.     

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 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.     

1-Butyne microwave spectrum,barrier to internal rotation,and molecular dipole moment

Measurements of rotational transitions of 1-butyne have been made in the range of ～20–130 GHz. Both a-type transitions up to J = 46 and b-type transitions up to J = 42 have been measured and fitted to a rotational Hamiltonian which includes centrifugal distortion terms. In addition to the five quartic centrifugal distortion constants, three sextic coefficients had to be included to reproduce the observed frequencies to within experimental error. The results of the analysis are sufficient for the prediction of all strong transitions throughout the millimeterwave range. A barrier to internal rotation of the methyl group of 3.260 kcal/mole (1 kcal/mole = 4.18 kJ/mole) has been derived from the first excited torsional state. Analysis of the second-order Stark effect has led to an accurate determination of both μ_a and μ_b with μ_a = 0.763(3) D and μ_b = 0.170(4) D.     

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.     

Millimeter- and Submillimeter-Wave Spectra of CD2F2

The millimeter- and submillimeter-wave spectrum of ¹³CD₂F₂ present in natural abundance in methylene fluoride-d₂ (CD₂F₂) has been measured in the region 230-380 GHz. The spectrum was recorded using a frequency-modulated millimeter- and submillimeter-wave spectrometer. More than 200 rotational transitions in the ground state of ¹³CD₂F₂ with J≤45 and K_a≤8 have been assigned. A combined weighted least squares fit of the newly assigned transitions with previously reported microwave data has been carried out in the Watson's A- and S-reduced Hamiltonian. The data have been fitted with a standard deviation approaching the experimental accuracy, to provide improved values for the rotational and quartic centrifugal distortion constants, including sextic distortion constants for the ground state of ¹³CD₂F₂.