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.     

Reinvestigation of microwave spectrum of dimethyl ether and rs structures of analogous molecules

Microwave spectra of dimethyl ether and its sixteen isotopic species have been measured. For species with singlet spectra, a least-squares analysis of observed transition frequencies gave rotational and five quartic centrifugal distortion constants. For species with multiplet spectra due to the methyl internal rotation, a least-squares analysis of observed multiplet frequencies gave not only unperturbed rotational and five quartic centrifugal distortion constants but also the quantities related to the methyl internal rotation. The r_s structures from (CH₃)₂O, CH₃OCD₃, and (CD₃)₂O species as the parent species, respectively, were compared with one another. The proposed r_s structure has been established from all the species measured and was compared with the r_s-like structure obtained by a diagnostic least-squares method and with the reported structure. The r_s structure of the present molecule was compared with the reported structures of dimethyl sulfide and dimethyl silane in relation to the tilt phenomenon. The r_s structure of dimethyl sulfide was revised based on the present comparison.     

Millimeter-wave spectroscopy of rare isotopomers of HC5N and DC5N: determination of a mixed experimental-theoretical equilibrium structure for cyanobutadiyne

Cyanobutadiyne has been produced by gas phase copyrolysis of pyridine and phosphorus trichloride in a flow reactor. The yield of the reaction is sufficiently good to allow the detection of rotational transitions of the ¹³C and ¹⁵N containing species in natural abundance. Normal pyridine and its fully deuterated variant have been used as precursors, making it possible to study the ground-state rotational spectra of 14 isotopomers in the millimeter wave region. Very accurate values of the rotational and quartic centrifugal distortion constants have been obtained for all the isotopic species investigated, and in addition the sextic distortion constant has been precisely determined for the most abundant variants H¹²C₅¹⁴N and D¹²C₅¹⁴N, for which the measurements have been extended up to 460 GHz. A mixed experimental-theoretical equilibrium structure has been evaluated for cyanobutadiyne combining experimental ground-state rotational constants with theoretically computed zero-point contributions. The r_e geometry is compared with operationally defined purely experimental structures, namely r₀, r_s, and r_m⁽¹⁾ molecular structures.     

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.     

Molecular beam electric resonance study of KCN,K13CN and KC15N

The microwave spectra of the isotopic species K¹³CN and KC¹⁵N have been investigated by molecular beam electric resonance spectroscopy, using the seeded beam technique. For both isotopic species about 20 rotational transitions originating in the ground vibrational state were observed in the frequency range 9–38 GHz. The observed transitions were fitted to an asymmetric rotor model to determine the three rotational, as well as the five quartic and three sextic centrifugal distortion constants. The hyperfine spectrum of KCN has been unravelled with the help of microwave-microwave double-resonance techniques. One hundred and forty hyperfine transitions in 11 rotational transitions have been assigned. The hyperfine structures of K¹³CN and KC¹⁵N were also studied. For all three isotopic species the quadrupole coupling constants and some spin-rotation coupling constants could be deduced. The rotational constants of the ¹³C and ¹⁵N isotopically substituted species of potassium cyanide, combined with those of the normal isotopic species (determined more accurately in this work), allowed an accurate and unambiguous evaluation of the structure, which was confirmed to be T shaped. Both the effective structure of the ground vibrational state and the substitution structure were evaluated. The results for the effective structural parameters are $\text{r}{}_{\mathrm{<mtext>CN</mtext>}}\text{= 1.169(3)}\text{A}\text{?}$, $\text{r}{}_{\mathrm{<mtext>KC</mtext>}}\text{= 2.716(9)}\text{A}\text{?}$, and $\text{r}{}_{\mathrm{<mtext>KN</mtext>}}\text{= 2.549(9)}\text{A}\text{?}$. The values obtained for the principal hyperfine coupling constant eQq_z(N), the angle between the CN axis and z_N, and the bond length r_CN indicate that in gaseous potassium cyanide the CN group can be considered as an almost unperturbed CN^? ion.     

The millimeterwave spectrum of germyl fluoride: Determination and comparison of the effective, substitution, and equilibrium structures

The ground state rotational spectrum of germyl fluoride was measured up to 1273 GHz (J ≤ 63). The rotational constants and quartic and sextic centrifugal distortion constants have been determined accurately for five isotopic species in natural abundance (^{70/72/73/74/76}Ge). The high accuracy of the rotational constants of these five isotopomers allowed us to study the mass dependence of the substitution coordinate of Ge. Equilibrium rotational constants of ⁷⁴GeH₃F were deduced with the help of the axial rotational constant and the rotation-vibration interaction constants determined by high resolution infrared spectroscopy. The r₀, r_,I, and r_e structures of GeH₃F were determined.     

Reinvestigation of Microwave Spectrum of Ethylsilane: I. Structure and Dipole Moment

Microwave spectra of ethylsilane and its 19 isotopic species have been measured. A least-squares analysis of the observed frequencies gave rotational constants and three quartic centrifugal distortion constants. The r_s structure has been well established from the moments of inertia calculated from the observed rotational constants. The structure has also been obtained from the differences of the observed moments of inertia between the isotopic and normal species by the diagnostic least-squares method. The structure of trans-propylsilane has been established from the reported and newly observed rotational constants for the isotopically substituted species of this molecule by application of the so-called diagnostic least-squares method. The structual parameters of ethylsilane were compared with those of analogous molecules. Special attention was paid to the C-C bond length. The newly obtained bond length is r(C-C)=1.541±0.001 Å. The dipole moment and its direction in the molecule were determined from Stark-effect measurements of several low-J transitions by the usual perturbation method; μ_a=0.733±0.001 D, μ_b=0.349±0.003 D, and μ_total=0.812±0.002 D were obtained for the normal species. The angle between the dipole moment and the Si-C bond was 36′ toward the inside of the molecule. These values were compared with those of analogous molecules.     

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.     

The microwave spectrum and structure of carbonyl fluoride

The ground state microwave rotational spectra of four isotopic species of carbonyl fluoride have been measured between 18 GHz and 77 GHz, and analyzed to obtain the quartic and some sextic centrifugal constants. The rotational constants have been used to obtain a r₀ structure and, using a harmonic force field, a r_z structure is also obtained: r_z(C---F) = 1.3166 (10) Å, r_z(C---O) = 1.1700 (26) Å.These values are considerably more precise than those of the previously estimated average structure.     

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 of silyl isocyanate, SiH3NCO: Spectra of isotopically substituted species and correction of the rs structure

Microwave spectra have been measured for 10 isotopic species of silyl isocyanate, SiH₃NCO, in the ground vibrational state, and in several excited states of the lowest frequency bending vibration, ν₁₀. This vibration is highly anharmonic, with a potential hump of 31.5 cm⁻¹ at the linear configuration, and its effects have been removed from the rotational constants to produce effective ground-state rotational constants B₀^* for each isotopic species. These B₀^* constants have been used to determine the structural parameters, which are now in good agreement with earlier electron diffraction values. Excellent predictions have been made of the centrifugal distortion constants for different isotopic species and vibrational states, as well as of the l-type doubling constants of the various isotopic species.     

The harmonic force field and ground-state average structure of difluoroborane

An improved harmonic force field of difluoroborane has been calculated using the vibrational wavenumbers and quartic centrifugal distortion constants of four isotopic species. The unidentified vibrational mode ν₅ is predicted at 1049 ± 50 and 775 ± 50 cm⁻¹ for HBF₂ and DBF₂, respectively. The ground-state average structure of HBF₂ has been found to be r_z(BH) = 1.195 ± 0.003 Å; r_z(BF) = 1.315 ± 0.001 Å; (FBF) = 118.0 ± 0.1°.     

The force field and rz structure of Ketene

Recently determined Coriolis coupling constants for H₂ and D₂ Ketene, centrifugal distortion constants for H₂, HD, and D₂ Ketene have enabled 16 of the 19 parameters in the general force field of Ketene to be determined with significance, the ambiguity between the choice of two sets of A₁ and B₁ species force constants being removed. The r₀ structure has been redetermined using the latest values of the rotational constants of H₂, HD, and D₂ Ketene and an r_z structure has been determined for the first time.     

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.     

Molecular structure and centrifugal distortion constants of isocyanic acid from the microwave,millimeter wave,and far-infrared spectra

The pure rotational spectra of HNCO and DNCO were measured in the far-infrared region from 80 to 350 cm^?1 by a Fourier transform spectrometer with a resolution of 0.1 cm^?1. The ^rR_K branches were measured and assigned for HNCO from K = 1 to 6, and for DNCO from K = 3 to 8. The measured transition wavenumbers were analyzed together with the microwave and millimeter wave data reported by Hocking, Gerry, and Winnewisser [Can. J. Phys.53, 1869–1901 (1975)] and with the far-infrared data of Krakow, Lord, and Neely [J. Mol. Spectrosc.27, 148–176 (1968)] in the low-wavenumber region. The microwave and millimeter wave data of H¹⁵NCO, HN¹³CO, and HNC¹⁸O reported by Hocking et al. were reanalyzed assuming several centrifugal distortion constants to be identical with those of the normal species. The molecular structure of HNCO was reevaluated using a modified substitution method from the rotational constants obtained in this work. The molecule has a bent structure in a trans configuration with $\text{r}\text{(NH) = 0.995}\text{A}\text{?}$, $\text{r}\text{(NC) = 1.314}\text{A}\text{?}$, $\text{r}\text{(CO) = 1.668}\text{A}\text{?}$, ∠HNC = 123.9°, and ∠NCO = 172.6°.     

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.     

The microwave spectrum of α-d2 oxetane and the analysis of the centrifugal distortion constants of oxetane

The microwave spectrum of the α-d₂ isotopic species of oxetane (trimethylene oxide) has been observed from 26.5 to 40.0 GHz. About 60 lines have been assigned for each of v = 0 to v = 5 in the puckering vibration. The spectra have been interpreted using an effective hamiltonian for each vibrational state including four of the five quartic distortion constants according to Watson's formulation. In general, the lines are fitted to better than ±10 kHz.The zig-zag dependence of the distortion constants on the puckering vibrational quantum number has been quantitatively analyzed for the parent, α-d₂, αα′-d₄, d₆, and α-d₂ species of oxetane and has yielded values for the $\text{a}{}_{\mathrm{<mtext>pucker</mtext>}}{}^{\mathrm{\alpha \beta }}$ constants of these isotopic species.     

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.     

Diode laser spectrum and analysis of the 882-cm−1 band of s-tetrazine

A high-resolution diode laser spectrum of the 882-cm^?1 band of s-tetrazine has been obtained. A complete rotational analysis of this band, incorporating quartic and sextic centrifugal distortion coefficients, has been carried out. The rotational constants A, B, and C have been determined with an accuracy better than 10^?5 cm^?1. The analysis has shown the band to be A-type and, on this basis, the vibrational assignment of this band has been revised from ν₁₂ to ν₁₄.