Ground-state Rotational Spectra Research Articles

Effect of weakening the hydrogen bond on the angular geometry of H2CO⋅⋅⋅HX: Evidence from the rotational spectrum of H2CO⋅⋅⋅HCN

The ground-state rotational spectra of three isotopic species (H2CO⋅⋅⋅HC14N, H2CO⋅⋅⋅HC15N, and H2CO⋅⋅⋅DC14N) of the formaldehyde–hydrogen cyanide dimer have been observed by pulsed-nozzle, Fourier-transform microwave spectroscopy. Analysis of the spectra yielded rotational constants, centrifugal distortion constants, and 14N-nuclear quadrupole coupling constants which for the species H2CO⋅⋅⋅HC14N have the following values: A0=91.2(7.5) GHz, B0=1785.6217(10), C0=1749.7215(10) MHz, ΔJ =4.76(2) kHz, ΔJK=−6.1181(7) MHz, δJ =2.58(1) kHz, χaa=−4.381(3) MHz, and χbb =2.141(4) MHz. The spectroscopic constants have been interpreted to establish a planar geometry for the dimer in which HCN forms a hydrogen bond to O in H2CO. The angle between the C=O bond and HCN symmetry axis is θ=138.1 deg, and the intermolecular distance from O to C is r(O⋅⋅⋅C)=3.271 Å. The difference in the angle θ between H2CO⋅⋅⋅HCN and H2CO⋅⋅⋅HF is discussed on the basis of a simple model for the hydrogen bond in these dimers.

An investigation of the hydrogen-bonded dimer H3N⋅⋅⋅HBr by pulsed-nozzle, Fourier-transform microwave spectroscopy of ammonium bromide vapor

The ground-state rotational spectrum of a dimer of ammonia and hydrogen bromide has been detected by using the technique of Fourier-transform microwave spectroscopy in a Fabry–Perot cavity to examine a supersonically expanded gas pulse composed of ammonium bromide vapor entrained in argon. The spectroscopic constants B0, DJ, DJK, χ(14N), χ(79Br), and χ(81Br) have been determined (where appropriate) for the four symmetric-top type isotopic species (14NH3, H79Br), (14NH3, H81Br), (15NH3, H79Br), and (15NH3, H81Br) and for the first of these the values are as follows: B0=3226.862(1) MHz, DJ=9.0(2) kHz, DJK=142.2(6) kHz, χ(14N)=−3.183(8) MHz, and χ(79Br)=361.245(6) MHz. The spectroscopic constants have been interpreted in terms of a hydrogen-bonded dimer of C3v symmetry, having r(N⋅⋅⋅Br)=3.255 Å and the hydrogen-bond stretching force constant kσ=13.4 N m−1. A detailed analysis has demonstrated that χ(79Br) is consistent with a model of the dimer in which only a small electrical rearrangement in the HBr subunit occurs on dimer formation (as opposed to proton transfer to NH3) and that this can be viewed as the transfer of ∼0.le from H into the 4pz orbital of Br.

The geometry and intermolecular stretching force constant of the dimer of carbonyl sulphide and hydrogen cyanide as determined by rotational spectroscopy

The ground-state rotational spectra of four isotopic species of the carbonyl sulphide—hydrogen cyanide dimer have been observed and measured by using pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectroscopic constants B 0, D J and χ( 14N) have been determined as follows. Spectroscopic constant (OC 32S, HC 14N) (OC 34S, HC 14N) (OC 32S, DC 14N) (OC 32S, HC 15N) B 0 (MHz) 759.1867(2) 742.7109(3) 753.7077(2) 737.9376(1) D J (kHz) 0.576(2) 0.566(4) 0.550(2) 0.538(1) χ( 14N) (MHz) −4.31(14) −4.28(15) −4.56(13) − The rotational constants are interpreted in terms of a linear, hydrogen-bonded geometry SCO⋯HCN with r(O⋯C) = 3.346(12) Å. The intermolecular stretching force constant is found to have the value k σ = 3.2 N m −1.

The rotational spectrum and molecular geometry of an antihydrogen-bonded dimer of sulfur dioxide and hydrogen cyanide

The ground-state rotational spectra of the four isotopic species (32SO2,HC14N), (32SO2,DC14N), (32SO2,HC15N), and (34SO2,HC14N) of a weakly bound dimer of sulfur dioxide and hydrogen cyanide have been observed by means of pulsed-nozzle, Fourier-transform microwave spectroscopy. The 14N-nuclear quadrupole coupling constants determined for the isotopomer (32SO2,HC14N) of this asymmetric rotor molecule are χaa =−2.876(3) MHz and χbb =2.025(4) MHz while the rotational and centrifugal distortion constants are (A0−ΔK) =8633.849(1) MHz, B0=1848.890(2) MHz, C0=1615.863(2) MHz, ΔJ =9.56(1) kHz, ΔJK =114.84(7) kHz, δJ =0.838(6) kHz, and δK =89(1) kHz. The spectroscopic constants have been interpreted in terms of a nonplanar, antihydrogen-bonded geometry of Cs symmetry with S, H, C, and N nuclei lying in the symmetry plane. The HCN molecule is roughly perpendicular to the plane of the SO2 molecule with N lying between the SO2 plane and the H atom. The distance between the SO2 and HCN centers of mass is rc.m. =3.6542(1) Å. The angle between the C2 axis of the SO2 subunit and the NCH axis is 86° and the two axes intersect at a distance of 1.38 Å above the S nucleus.

Rotational spectrum, H, 19F spin–spin and D–nuclear quadrupole coupling constants, and molecular geometry of the sulphur dioxide–hydrogen fluoride dimer

The ground state rotational spectra of three isotopic species 32SO2⋅⋅⋅HF, 32SO2⋅⋅⋅DF, and 34SO2⋅⋅⋅HF of a dimer formed between sulphur dioxide and hydrogen fluoride have been detected and measured using a pulsed-nozzle, Fourier-transform microwave spectrometer. An analysis of observed nuclear hyperfine structure leads to the H, 19F nuclear spin–nuclear spin coupling constants DHFaa =−190(2) kHz and (DHFbb−DHFcc) =−57(4) kHz for 32SO2⋅⋅⋅HF, and to the D-nuclear quadrupole coupling constants χaa =227(3) kHz and (χbb−χcc) =68(13) kHz for 32SO2⋅⋅⋅DF. Rotational and centrifugal constants have been determined for all three isotopic species, with the following values for 32SO2⋅⋅⋅HF: A0=16 502.775(4) MHz, B0=2100.308(1) MHz, C0=1853.642(1) MHz, ΔJ =18.31(2) kHz, ΔJK =−521.78(4) kHz, and δJ =4.37(3) kHz. The rotational constants for the three isotopic species are interpreted in terms of a planar geometry in which hydrogen fluoride forms a cis hydrogen bond to one of the oxygen atoms of SO2. Assuming a linear hydrogen bond and unchanged subunit geometries, it is found that r(O⋅⋅⋅F)=2.818(8) Å and θ=215.1° where θ is the S=O⋅⋅⋅H bond angle. The nuclear hyperfine coupling constants are shown to be consistent with this arrangement.

The ground state rotational spectrum of difluoromethane

The ground state rotational spectrum of difluoromethane

Centrifugal Distortion and Internal Rotation Analysis of the Rotational Spectrum of Methyl Thiocyanate

The ground state rotational spectrum of methyl thiocyanate has been investigated between 7 and 300 GHz (J ≦ 38 and K_ ≦ 25). An overall fit of the measurements using the Internal Axis Method has allowed us to accurately determine the internal rotation parameters. For the A substate effective rotational parameters are given which allow the calculation of transition frequencies of possible astrophysical interest.

The millimeter wave spectrum of cyanoallene, CH2CCHCN, using a new digital lock-in technique

The ground state rotational spectrum of cyanoallene, CH2CCHCN, has been observed in the frequency region 87–178 GHz. Over 210 a-type and 10 b-type transitions have been identified. The rotational constants and all quartic, sextic, and several higher-order centrifugal distortion constants have been determined using Watson's S-reduced Hamiltonian. The millimeter wave spectra were recorded with the frequency-modulated output of a phase-locked klystron source, followed by a frequency multiplier. The detector signal was demodulated with a newly constructed digital lock-in amplifier.

Erratum

Proc. R. Soc. Lond. A 401, 327-347 (1985) Spectroscopic investigations of hydrogen bonding interactions in the gas phase. X. Properties of the hydrogen-bonded heterodimer HCN⋯HF determined from hyperfine coupling and centrifugal distortion effects in its ground-state rotational spectrum By A. C. Legon, D. J. Millen and L. C. Willoughby On p. 327, at the end of the abstract, for 0.14 Å read 0.014 Å. On p. 343, line 7, for 0.025 Å read 0.014 Å. On p. 344, line 27, for 25.4° read 21.7°; line 33, for 6.6° read 2.9°. On p. 347, line 12, for 0.025 Å read 0.014 Å.

The rotational spectrum, geometry, and intermolecular force constant of the heterodimer of hydrogen cyanide and fluoroform

The ground-state rotational spectra of six isotopic species of an intermolecular complex formed by hydrogen cyanide and fluoroform have been measured using the pulsed-nozzle, Fourier-transform microwave technique. The rotational constant B0, the centrifugal distortion constants DJ,DJK,HJ, HJK, and HKJ, and, where appropriate, the nuclear quadrupole coupling constants χ(14N) and χ(D) have been determined for each of the species HC14N⋅⋅⋅HCF3, DC14N⋅⋅⋅HCF3, HC14⋅⋅⋅DCF3, HC15N⋅⋅⋅HCF3, HC15N⋅⋅⋅DCF3, and DC15N⋅⋅⋅HCF3. For HC14N⋅⋅⋅HCF3 the values are as follows: B0=1151.2991(4) MHz, DJ=1.91(1) kHz, DJK=282.75(6) kHz, HJ=−0.1(1) Hz, HJK=44.3(5) Hz, HKJ=53(5) Hz, and χ(14N)=3.948(8) MHz. The form of the spectra and magnitudes of the rotational constants allow the conclusion that the geometry of the complex is of C3V symmetry with the nuclei in the order HCN⋅⋅⋅HCF3 and lead to r(N⋅⋅⋅C)=3.489(2) Å for HCF3 species but 3.483(1) Å for DCF3 species. The intermolecular stretching force constant determined from DJ is kσ=3.52 N m−1.

Spectroscopiċ investigations of hydrogen bonding interactions in the gas phase. X. Properties of the hydrogen-bonded heterodimer HCN∙ ∙ ∙HF determined from hyperfine coupling and centrifugal distortion effects in its ground-state rotational spectrum

The rotational spectra of six isotopic species of HCN∙ ∙ ∙HF in their vibrational ground states have been observed by pulsed-nozzle, Fourier-transform, microwave spectroscopy and have been analysed to yield the rotational constants B 0 , centrifugal distortion constants D J and various hyperfine coupling constants X i (D), X 3 ( 14 N) and D 4, 5 as follows (subscripts refer to the numbering scheme H (1) C (2) N (3) ∙ ∙ ∙H (4) F (5) ). isotopic species B 0 / MH Z D J /kH Z X i (D)/kH Z X 3 ( 14 N)/MH Z D 4, 5 (H, F)/kH Z HC 15 N∙ ∙ ∙HF 3573 5874(2) 6.97(2) ─ ─ –242(6) HC 15 N∙ ∙ ∙DF 3551.5110 6.83 269(4)( i = 4) ─ ─ HC 14 N∙ ∙ ∙HF 3591.1552 6.99 ─ –4.098(4) –218(6) HC 14 N∙ ∙ ∙DF 3569.6576 6.86 259(2)( i = 4) –4.096(1) ─ DC 15 N∙ ∙ ∙HF 3360.3549 5.85 186(5)( i = 1) ─ –244(4) DC 15 N∙ ∙ ∙DF 3338.0824 5.81 { 181(10) ( i = 1) ─ ─ 283(7) ( i = 4) The B 0 values lead to conclusions about the dimer geometry, the D J values allow the hydrogen bond stretching force constant k σ to be determined and the hyperfine coupling constants provide information about the internal dynamics of the subunits. An analysis of the D nuclear quadrupole coupling and H, F nuclear spin nuclear-spin coupling constants demonstrates that the H—F bond lengthens by 0.14 Å when the heterodimer HCN∙ ∙ ∙HF is formed. (1 Å = 10 –10 m = 10 –1 nm.)

33S-nuclear quadrupole coupling in the rotational spectrum of the weakly bound dimer SCO … HF

The ground-state rotational spectra of four isotopically substituted species of SCO … HF have been observed and measured by the technique of pulsed-nozzle, Fourier-transform microwave spectroscopy. The following values of the spectroscopic constants B 0, D J and χ( 33S) have been determined for this linear molecule: ▪ An interpretation of the 33S-nuclear quadrupole coupling constant χ( 33S) allows a description of the dynamics of the SCO submit while the rotational constants B o leads to r(O … F) = 2.9234(4)Å and the centrifugal distortion constants D J to k O = 2.83(2) N m −1

The rotational spectrum and properties of N2 ⋅⋅⋅ HCN

The ground state rotational spectra of eight isotopic species of a weakly bound dimer N(1)N(2) ⋅⋅⋅ HCN(3) formed between molecular nitrogen and hydrogen cyanide have been detected and measured by the technique of pulsed-nozzle, Fourier-transform microwave spectroscopy. Rotational constants B0, centrifugal distortion constants DJ, and, where appropriate, nuclear quadrupole coupling constants χn(14N) and χ(D) have been determined. For the five isotopic species containing 14N nuclei the results are: An analysis of the B0 values shows that the equilibrium geometry is linear, or nearly so, with the nuclei in the order shown. The DJ values lead to kσ=2.39 N m−1 for the intermolecular stretching force constant while the difference χ1(14N)–χ2(14N) is interpreted in terms of a transfer of 0.016 e from N(1) to N(2) when the complex is formed in the zero-point state.

The Rotational Spectrum of Propane Centrifugal Distortion Analysis

The ground state rotational spectrum of propane has been investigated between 6.4 and 26.5 GHz with a microwave Fourier transform spectrometer and between 140 and 300 GHz with a millimeter-wave spectrometer. High J transitions have been measured and fitted to a centrifugally distorted Hamiltonian including some sextic coefficients. The results of the analysis are sufficiently accurate for the prediction of all strong transitions of astrophysical interest.

Rotational spectrum of a weakly bound dimer of carbonyl sulphide and hydrogen chloride

The ground-state rotational spectra of five isotopic species of a weakly bound dimer formed by OCS and HCl in the gas phase have been investigated by pulsed-nozzle, Fourier-transform microwave spectroscopy. The observed spectra have been interpreted in terms of a linear (or nearly linear) equilibrium geometry with nuclei in the order SCO⋯HCl and lead on analysis to the following spectroscopic constants: [graphic omitted]. The values of DJ lead to kσ= 1.19 N m–1 for the intermolecular stretching force constant, while the rotational constants B0 give r(O⋯Cl)= 3.4787 (1)A for the species containing protium and r(O⋯Cl)= 3.4751 (1)A for the species containing deuterium.

Rotational spectrum and properties of the hydrogen-bonded heterodimer H 2 O· · · HCN from pulsed-nozzle, Fourier-transform microwave spectroscopy

The ground state rotational spectrum of a hydrogen-bonded heterodimer formed from water and hydrogen cyanide has been detected and measured by using the technique of pulsed-nozzle, Fourier-transform microwave spectroscopy. Rotational constants ( B 0 , C 0 ) centrifugal distortion constants ( ∆ J , ∆ JK ) and, where appropriate, 14 N-, D- or 17 O-nuclear quadrupole coupling constants have been determined for the following isotopic species; H 2 16 O· · · HC 14 N, H 2 18 O· · · HC 14 N, H 2 16 O· · · HC 15 N, HD 16 O· · · HC 15 N, D 2 16 O· · · HC 15 N, H 2 16 O· · · DC 15 N, HD 16 O· · · DC 15 N and H 2 17 O· · · HC 15 N. An analysis of these spectroscopic constants indicates that the heterodimer is effectively planar, with a pair of equivalent protons and the arrangement H 2 O· · · HCN. The intermolecular interaction is through a hydrogen bond between HCN and H 2 O and the distance between the O and C nuclei r (O· · · C) is 3.157 Å (1Å = 10 -10 m). An interpretation of the nuclear quadrupole coupling constants leads to the conclusion that arccos <cos 2 Φ > ½ ≈ 51°, where Φ is the angle between the local C 2 axis of H 2 O and the a -axis of the complex; and that arccos <cos 2 θ > ½ ≈ 10°, where θ is the angle between the HCN axis and the a -axis. The intermolecular stretching force constant k σ = 11 Nm -1 has been determined from ∆ J .

The ν3 fundamental bands of HN+2, DN+2, and DCO+

The ν3 (N–N or C–O stretch) fundamental bands of HN+2,DN+2, and DCO+ in the 5 μm region have been studied using a tunable infrared diode laser source. The absorption cell was a large liquid-nitrogen-cooled hollow cathode, and a discharge modulation scheme was used to enhance sensitivity and discriminate in favor of molecular ions. We observed 22 transitions for HN+2, 10 transitions for DN+2, and 15 transitions for DCO+. The analyses were straightforward because ground state rotational spectra are known for all three species. The resulting experimental ν3 band origins are 2257.8667(13), 2024.0141(13), and 1904.0640(20) cm−1, and the α3 (≡B″–B′) values are 329.7(12), 239.0(13), and 206.6(12) MHz for HN+2,DN+2, and DCO+, respectively.

The rotational spectrum of the weakly bound molecular complex OC ··· HCN investigated by pulsed-nozzle, Fourier-transform microwave spectroscopy

Abstract The technique of pulsed-nozzle, Fourier-transform microwave spectroscopy has been used to detect and assign the ground-state rotational spectrum of each of eleven isotopic species of a weakly bound molecular complex formed by carbon monoxide and hydrogen cyanide. The nature of the spectra is consistent with a linear complex. Accurate values of the rotational constants B0, the centrifugal distortion constants DJ and, where appropriate, the nuclear quadrupole coupling constant χaa(14N) or χaa(D) have been determined. For the most abundant species 16O12C ··· H12C14N, the results are: B0 = 1476.2925(1) MHz, DJ = 3.306(2) kHz and χaa(14N) = −4.285(1) MHz. When the B0 values are interpreted in terms of a simple model in which the nuclei are collinear in the order OC ··· HCN at equilibrium but with each rigid subunit executing a large amplitude oscillatory motion with respect to its centre of mass in the zero-point state, the mean values r(C ··· C) = 3.6698(2) and 3.66510(3)Aresult for the H- and D-bonded species, respectively. The intermolecular stretching force constant ka and the amplitude φav for the oscillation of the HCN subunit have been estimated from the spectroscopic constants DJ and χaa(14N), respectively.

Geometry of a weakly bound complex (H2S, HCN) determined from an investigation of its rotational spectrum

The ground-state rotational spectra of 10 isotopic species of a weakly bound complex formed by H2S and HCN in the gas phase have been investigated by the technique of pulsed-nozzle, Fourier-transform microwave spectroscopy. The following rotational constants, ½(B0+C0), centrifugal distortion constants, DJ, and 14N nuclear quadrupole coupling constants, χaa, have been determined: [graphic omitted] Analysis of the constants ½(B0+C0) shows that they are consistent only with a geometry of the complex in which the HCN molecule acts as a proton donor in forming a hydrogen bond to the S atom of H2S. The S, C and N nuclei are collinear (or nearly so), with r(S⋯C)= 3.8088 A and with the angle ϕ between the S⋯HCN line and the plane of the H2S subunit equal to 84.5°.

Vibronic Ground State Rotational Spectrum of 3-Bromothiophene

The rotational spectrum of 3-bromothiophene was investigated in the frequency range between 8 and 18 GHz by use of a microwave Fourier transform spectrometer. Both a- and b-type spectra were assigned for the vibronic ground state. Rotational constants, quartic centrifugal distortion constants and quadrupole coupling constants were obtained for the 79Br- and 81Br-isotopic species. For the analysis, the effective rotational Hamiltonian including centrifugal distortion in the form of Van Eijck's symmetric top reduction and bromine quadrupole coupling was set up in the coupled basis of the limiting symmetric top, J, K, I, F, MF>, and was diagonalized numerically. Spin rotation interaction was neglected