Centrifugal Distortion Constants ΔJ Research Articles

Microwave rotational spectrum of a weakly bound complex formed by hydrogen sulphide and hydrogen chloride

A weakly bound dimer formed by hydrogen sulphide and hydrogen chloride has been identified in the gas phase by means of its rotational spectrum which has been detected with the aid of the sensitive technique of pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectra of eight isotopic species have been analysed to give rotational constants (B0+C0), centrifugal distortion constants DJ and Cl nuclear quadrupole coupling constants Xaa as follows: [graphic omitted]The listed spectroscopic constants allow us to establish that the weak intermolecular linkage occurs through a hydrogen bond, with HCl acting as the proton donor and the S atom acting as the proton acceptor. The S⋯H—Cl nuclei are collinear (or nearly so) with r(S⋯Cl)= 3.8092 A, and the plane of the H2S molecule is almost perpendicular (ϕ= 93.8°) to the line of the hydrogen bond. Conclusions about the relative strength of the hydrogen bond are drawn from analyses of the constants DJ and Xaa.

ChemInform Abstract: MICROWAVE SPECTRUM, STRUCTURE, AND QUADRUPOLE COUPLING FOR THE ETHYLENE‐HYDROGEN CYANIDE COMPLEX

Microwave spectra for the complexes ethylene–HCN and ethylene–DCN were observed with the pulsed beam, Fourier transform spectrometer. The complexes are ‘‘T’’ shaped with the HCN hydrogen atom adjacent to the C–C double bond of ethylene. The HCN molecule lies on a line perpendicular to the plane of ethylene and passing through the ethylene center of mass. The HCN carbon atom is 3.702(10) A above the ethylene plane. The nitrogen quadrupole coupling strength is eQqaa(N)=−4.363(2) MHz for ethylene–HCN and eQqaa(N)=−4.396(3) MHz for ethylene–DCN. The deuterium quadrupole coupling strength is eQqaa(D)=0.178(7) MHz for ethylene–DCN. The anisotropy in the nitrogen quadrupole coupling eQ(qbb−qcc)(N) is 0.013(3) MHz for ethylene–HCN and 0.047(12) MHz for ethylene–DCN. The rotational constants are Centrifugal distortion constants DJ and DJK were obtained.

Rotational-vibration analysis of the n=0, nν6+ν1−nν6 subband in the hydrogen-bonded system 16O 12C ⋅⋅⋅ 1H 19F

Thirty-three P(J) branch and 15 R(J) branch transitions associated with the n=0, nν6+ν1−nν6 vibration in 16O 12C ⋅⋅⋅ 1H 19F have been assigned. Rotational constants B, centrifugal distortion constants DJ, rotational-vibrational interaction constant α1, and the frequency of the band origin ν0, have been determined as: B″=0.102 148(14)cm−1; B′=0.104 196(14) cm−1; D″J=3.6(1.8)×10−7 cm−1; D″J=3.8 (1.8)×10−7 cm−1; α1=−61.4(5) MHz; ν0=3844.0294 (50) cm−1. The spectrum is consistent with a linear complex having a hydrogen bond ν6 bending frequency of 75±12 cm−1 and excited state r(C⋅⋅⋅F) distance of 3.012 Å. A lower limit to the excited state lifetime is set at ≥2.8×10−10 s.

Microwave spectrum, structure, and quadrupole coupling for the ethylene–hydrogen cyanide complex

Microwave spectra for the complexes ethylene–HCN and ethylene–DCN were observed with the pulsed beam, Fourier transform spectrometer. The complexes are ‘‘T’’ shaped with the HCN hydrogen atom adjacent to the C–C double bond of ethylene. The HCN molecule lies on a line perpendicular to the plane of ethylene and passing through the ethylene center of mass. The HCN carbon atom is 3.702(10) Å above the ethylene plane. The nitrogen quadrupole coupling strength is eQqaa(N)=−4.363(2) MHz for ethylene–HCN and eQqaa(N)=−4.396(3) MHz for ethylene–DCN. The deuterium quadrupole coupling strength is eQqaa(D)=0.178(7) MHz for ethylene–DCN. The anisotropy in the nitrogen quadrupole coupling eQ(qbb−qcc)(N) is 0.013(3) MHz for ethylene–HCN and 0.047(12) MHz for ethylene–DCN. The rotational constants are Centrifugal distortion constants DJ and DJK were obtained.

8 3Kr nuclear quadrupole coupling, microwave spectrum, and structure of KrHCN

Rotational spectra have been observed for ten isotopic species of KrHCN using the pulsed Fabry–Perot Fourier transform technique. The 83Kr nuclear quadrupole coupling constant has been measured in 83KrHC 14N, 83KrHC 15N, and 83KrDC 14N. Values of the rotational constants B̄0, centrifugal distortion constants DJ and H, 14N and 83Kr nuclear quadrupole coupling constants are These constants are consistent with a linear or near-linear configuration, with a Kr–HCN center-of-mass separation of 4.54 Å, and the Kr atom located 27° off the HCN figure axis on average, where the vertex of this angle is placed on the HCN center-of-mass. KrHCN exhibits unusually large centrifugal distortion in comparison to previously studied Kr–hydrogen halide systems. We find that the measured 83Kr nuclear quadrupole coupling constants in 83KrHC 14N and 83KrDC 14N are consistent with a long range polarization model previously used to explain values of χKr in KrH(D)Cl and KrH(D)F.

The rotational spectrum and molecular properties of a hydrogen-bonded complex formed between hydrogen cyanide and hydrogen chloride

The rotational spectra of four isotopic species of a weak complex formed between HCN and HCl have been detected and analyzed by using the technique of Fourier-transform microwave spectroscopy conducted in a Fabry–Perot cavity with a pulsed nozzle molecular source. The rotational constants B̃0, centrifugal distortion constants DJ, and nuclear quadrupole coupling constants χaa that result are as follows: Interpretation of the spectroscopic constants leads to the conclusion that the atoms in the complex are colinear in the order HCN⋅⋅⋅HCl, with the weak binding through a hydrogen bond to the N atom HCN. Some quantitative details of the molecular geometry and intermolecular potential function have also been determined for the complex and are compared with those similarly obtained for other members of the series HCN⋅⋅⋅HX and the series B⋅⋅⋅HCl, where B is one of several different proton acceptors.

The rotational spectrum, 14N-nuclear quadrupole coupling constants, and H,19F nuclear spin–nuclear spin coupling constant of the cyanogen–hydrogen fluoride dimer

The microwave rotational spectra of four isotopic species of a linear dimer NCCN⋅⋅⋅HF formed between cyanogen and hydrogen fluoride have been observed and analyzed to give vibrational gound state rotational constants B0, centrifugal distortion constants DJ, the 14N-nuclear quadrupole coupling constants χ(1) and χ(2), and the H, 19F nuclear spin–nuclear spin coupling constants SHF as follows: It is shown that χ(1)−χ(2), which is necessarily zero in free cyanogen, arises from electrical changes rather than zero-point vibrational changes that accompany dimer formation. The part of this quantity assigned to polarization of cyanogen by hydrogen fluoride is interpreted on the basis of the Townes–Dailey model in terms of a transfer of ∼0.02e from N(1) to N(2) when HF approaches the latter atom along the molecular symmetry axis to form the dimer.

The rotational spectrum, H, 19F nuclear spin–nuclear spin coupling, D nuclear quadrupole coupling, and molecular geometry of a weakly bound dimer of carbon monoxide and hydrogen fluoride

A dimer formed between carbon monoxide and hydrogen fluoride has been detected and identified in the gas phase through its rotational spectrum by using a pulsed Fourier transform microwave spectrometer equipped with a pulsed nozzle source of the dimers and a Fabry-Perot cavity. Rotational constants B0, centrifugal distortion constants DJ, deuterium nuclear quadrupole coupling constants χD, and the nuclear spin–nuclear spin coupling constants SHF and SDF for the vibrational ground state of each of the five isotopic species investigated are as follows (the errors in B0 and DJ are discussed in the text): These spectroscopic constants have been interpreted in terms of a linear equilbrium geometry in which the atoms are in the order OC⋅⋅⋅HF and in which the weak binding is therefore through a hydrogen bond to the carbon atom. Various quantities characterizing the intermolecular interaction potential have also been estimated from the above constants and are used with those similarly determined to make comparison both within the series OC⋅⋅⋅HX (X = F, Cl, and Br) and among the different series B⋅⋅⋅HX (B = Ar, Kr, OC; X = F, Cl, and Br).

Aliev—Watson maxima—minima criteria for quartic centrifugal distortion constant DJ applied to several oblate rotor D6 h, D3 h and D3 d molecules

These criteria, together with the Kratzer diatomic approximation, are applied to the seven molecules C 6H 6, C 6D 6, C 6F 6, 11B 3N 3H 6, C 6H 3F 3, C 6H 12 and C 6D 12 and compared with reported experimental values. The hope of eliminating one or the other of the different experimental D J results, obtained by separately analyzing the R and S branch spectra for the same molecule, was not realized. The upper bound criterion did allow one pair of experimentally determined D J values for C 6H 6 and C 6D 6 to be rejected. In the course of rotational constant calculation it was noted that cyclohexane axial CH bonds tip 2.8° away from the three-fold axis rather than 2.8° toward this axis as reported earlier.

The High Resolution Rotational Spectrum of Silylbromide, SiH3 81Br

Abstract The microwave spectrum of SiH3 81Br has been reanalysed in the frequency range 8-40 GHz under high resolution. From 64 observed hyperfine transitions improved values for the rotational constant B = 4292646.2(4) kHz and the quadrupole coupling constant eqQ = 279825(5) kHz were obtained. Furthermore the centrifugal distortion constants DJ = 1.81(1) kHz and DJK = 29.19(4) kHz and the spin-rotation constants CN = -2.32(40) kHz and CK = -34.2(11) kHz were determined. From the values of CN and CK the 81Br nuclear shielding tensor is calculated. An improved value of ∣μ∣ - 1.319(8) D is given for the molecular electric dipole-moment.

Microwave spectra of 13CH3 12CD3 and 12CH3 13CD3 and the C–C bond length of ethane

We observed the J=2←1, K=1 transitions of two doubly labeled ethanes 13CH3 12CD3 and 12CH3 13CD3, which were contained in natural abundance in a CH3CD3 sample. The measured frequencies were subsequently made more accurate using enriched samples. Assuming the centrifugal distortion constants DJ and DJK, which were determined for 12CH3 12CD3, we calculated the B0 constants to be 16 088.428±0.030 and 16 251.914±0.030 MHz for 13CH3 12CD3 and 12CH3 13CD3, respectively. By combining these with the B0 of 12CH3 12CD3(16 474.438±0.030 MHz), we derived the rs distance of C–C to be 1.526131±0.000083 Å, where the error was due to uncertainties of the rotational constants. We also calculated the rz(C–C) distance to be 1.5312 Å in 12CH3 12CD3 by transferring Kuchitsu’s rz(C–H), rz(C–D), ϑz(CCH), and ϑz(CCD). We evaluated the dipole moments of the two species from the Stark effects to be 0.01067±0.00010 D and 0.01094±0.00011 D for 13CH3 12CD3 and 12CH3 13CD3, respectively, which were to be compared with 0.01078±0.00009 D of 12CH3 12CD3.

Microwave Spectrum of Ethyl Cyanide; r0-Structure, Nitrogen Quadrupole Coupling Constants and Rotation-Torsion-Vibration Interaction

An investigation of the microwave spectra of ethyl cyanide CH3CH2CN and the isotopes CH2DCH2CN, CH3CD2CN was carried out. The ground vibrational state of CH3CH2CN was reexamined under high resolution to give three centrifugal distortion constants DJ , DJK and DK. From the rotational constants of the ground vibrational state of CH3CH2CN, CH3CD2CN, CH2DCH2CN (symmetric) and CH2DCH2CN (asymmetric), CH3CH2 13CN and CD3CHDCN a r0-structure is derived. For the isotopes CH3CD2CN, CH2DCH2CN (symmetric) and CH2DCH2CN (asymmetric) the diagonal elements Χaa , Χbb and Χcc of the quadrupole tensor with respect to the principal axes of inertia were deduced from the hyperfine structure of the rotational lines. The off-diagonal element Χab for CH3CD2CN and CH2DCH2CN (symmetric) and the principal elements Χzz , Χxx of the quadrupole coupling tensor were obtained from Χaa, Χbb of the two molecules and from the principal axis rotation angle about the c-axis produced by isotopic substitution. For the analysis of the rotational spectra in the first excited states of methyl torsion and the lowest frequency in plane bending vibration of normal ethyl cyanide a molecular model with two internal degrees of freedom is considered. From the rotational line splittings in both states the coefficients V3 and V6 of the Fourier expansion of the potential hindering the internal rotation of the methyl group are determined.

Microwave Spectrum, Molecular Structure, Force Field, and Dipole Moment of Thiocarbonyl Selenide, SCSe

The microwave spectrum of SCSe was observed in the (0, 1±1, 0) and (0, 2±2, 0) vibrational states. The transitions observed were: J=7←6, 8←7, and 9←8 for 80Se and 78Se species, and J=8←7 and 9←8 for 76Se and 82Se species. It was not possible to observe directly the transitions of the ground state, but ground state rotational constants extrapolated from the two vibrationally excited states are 2043.310, 2060.321, 2078.190, and 2027.113 MHz for 32S12C80Se, 32S12C78Se, 32S12C76Se, and 32S12C82Se, respectively. These values differ considerably from those reported previously. The vibration-rotation constant α2 and the l-type doubling constant ql are also obtained as α2 = − 4.133, −4.169, − 4.215, and − 4.116 MHz, and ql=1.005, 1.021, 1.041, and 0.996 MHz for 32S12C80Se, 32S12C78Se, 32S12C76Se, and 32S12C82Se, respectively. The centrifugal distortion constant Dj was determined to be 0.163 and 0.22 kHz for 80Se and 78Se species. The molecular force field was calculated from ql to be fC–Se = 5.72, fC–S = 7.97, frr′ = 0.59, and fα/r1r2 = 0.20 mydn/Å. The dipole moment in the (0, 2±2, 0) state was measured to be 0.031 D.

Centrifugal distortion constants for difluoramine

The inertia tensor derivatives for a centre-of-mass principal axes system have been obtained for an XYZ2 type molecule of symmetry Cs. From the force field for difluoramine, the centrifugal distortion constants DJ, DJK, DK, R5, R6 and δJ have been calculated for NHF2 and NDF2 using a first-order perturbation theory. Except for R6, the other constants have values comparable with DJK, and thus a correction to the rigid-rotor energy levels should include all these terms.