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  • 1
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    Intramolecular competition between n-pair and π-pair hydrogen bonding: Microwave spectrum and internal dynamics of the pyridine–acetylene hydrogen-bonded complex (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-09-11
    Description: a -type rotational spectra of the hydrogen-bonded complex formed from pyridine and acetylene are reported. Rotational and 14 N hyperfine constants indicate that the complex is planar with an acetylenic hydrogen directed toward the nitrogen. However, unlike the complexes of pyridine with HCl and HBr, the acetylene moiety in HCCH—NC 5 H 5 does not lie along the symmetry axis of the nitrogen lone pair, but rather, forms an average angle of 46° with the C 2 axis of the pyridine. The a -type spectra of HCCH—NC 5 H 5 and DCCD—NC 5 H 5 are doubled, suggesting the existence of a low lying pair of tunneling states. This doubling persists in the spectra of HCCD—NC 5 H 5 , DCCH—NC 5 H 5 , indicating that the underlying motion does not involve interchange of the two hydrogens of the acetylene. Single 13 C substitution in either the ortho- or meta-position of the pyridine eliminates the doubling and gives rise to separate sets of spectra that are well predicted by a bent geometry with the 13 C on either the same side (“inner”) or the opposite side (“outer”) as the acetylene. High level ab initio calculations are presented which indicate a binding energy of 1.2 kcal/mol and a potential energy barrier of 44 cm −1 in the C 2 v configuration. Taken together, these results reveal a complex with a bent hydrogen bond and large amplitude rocking of the acetylene moiety. It is likely that the bent equilibrium structure arises from a competition between a weak hydrogen bond to the nitrogen (an n-pair hydrogen bond) and a secondary interaction between the ortho-hydrogens of the pyridine and the π electron density of the acetylene.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    A monomeric complex of ammonia and cuprous chloride: H3N⋯CuCl isolated and characterised by rotational spectroscopy and ab initio calculations (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-04-10
    Description: The H 3 N⋯CuCl monomer has been generated and isolated in the gas phase through laser vaporisation of a copper sample in the presence of low concentrations of NH 3 and CCl 4 in argon. The resulting complex cools to a rotational temperature approaching 2 K during supersonic expansion of the gas sample and is characterised by broadband rotational spectroscopy between 7 and 18.5 GHz. The spectra of six isotopologues are measured and analysed to determine rotational, B 0 ; centrifugal distortion, D J , D JK ; and nuclear quadrupole coupling constants of Cu, Cl, and 14 N nuclei, χ aa (X). The geometry of the complex is C 3v with the N, Cu, and Cl atoms located on the a inertial axis. Bond distances and the ∠(H —N⋯Cu) bond angle within the complex are precisely evaluated through fitting of geometrical parameters to the experimentally determined moments of inertia and through ab initio calculations at the CCSD(T)(F12*)/AVQZ level. The r (Cu —Cl), r (Cu —N), and ∠(H —N⋯Cu) parameters are, respectively, evaluated to be 2.0614(7) Å, 1.9182(13) Å, and 111.40(6)° in the r 0 geometry, in good agreement with the ab initio calculations. Geometrical parameters evaluated for the isolated complex are compared with those established crystallographically for a solid-state sample of [Cu(NH 3 )Cl].
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    A two force-constant model for complexes B⋯M–X (B is a Lewis base and MX is any diatomic molecule): Intermolecular stretching force constants from centrifugal distortion constants DJ or ΔJ (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-02-19
    Description: A two force-constant model is proposed for complexes of the type B⋯MX, in which B is a simple Lewis base of at least C 2 v symmetry and MX is any diatomic molecule lying along a C n axis ( n ≥ 2) of B. The model assumes a rigid subunit B and that force constants beyond quadratic are negligible. It leads to expressions that allow, in principle, the determination of three quadratic force constants F 11 , F 12 , and F 22 associated with the r (B⋯M) = r 2 and r (M–X) = r 1 internal coordinates from the equilibrium centrifugal distortion constants D J e or Δ J e , the equilibrium principal axis coordinates a 1 and a 2 , and equilibrium principal moments of inertia. The model can be applied generally to complexes containing different types of intermolecular bond. For example, the intermolecular bond of B⋯MX can be a hydrogen bond if MX is a hydrogen halide, a halogen-bond if MX is a dihalogen molecule, or a stronger, coinage-metal bond if MX is a coinage metal halide. The equations were tested for BrCN, for which accurate equilibrium spectroscopic constants and a complete force field are available. In practice, equilibrium values of D J e or Δ J e for B⋯MX are not available and zero-point quantities must be used instead. The effect of doing so has been tested for BrCN. The zero-point centrifugal distortion constants D J 0 or Δ J 0 for all B⋯MX investigated so far are of insufficient accuracy to allow F 11 and F 22 to be determined simultaneously, even under the assumption F 12 = 0 which is shown to be reasonable for BrCN. The calculation of F 22 at a series of fixed values of F 11 reveals, however, that in cases for which F 11 is sufficiently larger than F 22 , a good approximation to F 22 is obtained. Plots of F 22 versus F 11 have been provided for Kr⋯CuCl, Xe⋯CuCl, OC⋯CuCl, and C 2 H 2 ⋯AgCl as examples. Even in cases where F 22 ∼ F 11 (e.g., OC⋯CuCl), such plots will yield either F 22 or F 11 if the other becomes available.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Interaction of a pseudo-π C—C bond with cuprous and argentous chlorides: Cyclopropane⋯CuCl and cyclopropane⋯AgCl investigated by rotational spectroscopy and ab initio calculations (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-10-31
    Description: Strongly bound complexes (CH 2 ) 3 ⋯MCl (M = Cu or Ag), formed by non-covalent interaction of cyclopropane and either cuprous chloride or argentous chloride, have been generated in the gas phase by means of the laser ablation of either copper or silver metal in the presence of supersonically expanded pulses of a gas mixture containing small amounts of cyclopropane and carbon tetrachloride in a large excess of argon. The rotational spectra of the complexes so formed were detected with a chirped-pulse, Fourier transform microwave spectrometer and analysed to give rotational constants and Cu and Cl nuclear quadrupole coupling constants for eight isotopologues of each of (CH 2 ) 3 ⋯CuCl and (CH 2 ) 3 ⋯AgCl. The geometry of each of these complexes was established unambiguously to have C 2v symmetry, with the three C atoms coplanar, and with the MCl molecule lying along a median of the cyclopropane C 3 triangle. This median coincides with the principal inertia axis a in each of the two complexes (CH 2 ) 3 ⋯MCl. The M atom interacts with the pseudo-π bond linking the pair of equivalent carbon atoms F C (F = front) nearest to it, so that M forms a non-covalent bond to one C—C edge of the cyclopropane molecule. The (CH 2 ) 3 ⋯MCl complexes have similar angular geometries to those of the hydrogen- and halogen-bonded analogues (CH 2 ) 3 ⋯HCl and (CH 2 ) 3 ⋯ClF, respectively. Quantitative details of the geometries were determined by interpretation of the observed rotational constants and gave results in good agreement with those from ab initio calculations carried out at the CCSD(T)(F12*)/aug-cc-pVTZ-F12 level of theory. Interesting geometrical features are the lengthening of the F C— F C bond and the shrinkage of the two equivalent B C— F C (B = back) bonds relative to the C—C bond in cyclopropane itself. The expansions of the F C— F C bond are 0.1024(9) Å and 0.0727(17) Å in (CH 2 ) 3 ⋯CuCl and (CH 2 ) 3 ⋯AgCl, respectively, according to the determined r 0 geometries. The C—C bond lengthening is in each case about four times that observed by similar methods in the corresponding complexes of MCl with ethyne and ethene, even though the cyclopropane complexes are more weakly bound than their ethyne and ethene analogues. Reasons for the larger increase in r (CC) in the pseudo-π complexes are discussed.
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    Topics: Chemistry and Pharmacology , Physics
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  • 5
    Electronic Resource
    Electronic Resource
    An investigation of the trimethylammonium chloride molecule in the vapor phase by pulsed-nozzle, Fourier-transform microwave spectroscopy (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6867-6876 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground-state rotational spectra of the symmetric-top isotopomers [(CH3)314N, H35Cl], [(CH3)314N, D35Cl], [(CH3)315N, H35Cl], and [(CH3)315N, H37Cl] of a dimer formed between trimethylamine and hydrogen chloride have been observed in the vapor above heated samples of solid trimethylammonium chloride by pulsed-nozzle, Fourier-transform, microwave spectroscopy. Spectroscopic constants have been determined in each case and for [(CH3)314N, H35Cl] the values are B0=1800.4605(2) MHz, DJ=0.320(10) kHz, DJK=13.59(11) kHz, χ(35Cl)=−21.625(5) MHz, and χ(14N)=−3.504(5) MHz. The observed rotational constants B0 indicate that the nuclei N, H, and Cl lie along the C3 symmetry axis of the molecule in the order N⋅⋅⋅H⋅⋅⋅Cl with the distance r(N⋅⋅⋅Cl)=2.8164(3) A(ring). A comparison of the values of the nuclear quadrupole coupling constants χ(35Cl) and χ(14N) with those in related dimers and molecules leads to the evocation of some ionic character (CH3)3N +H C¯l arising from a significant extent of proton transfer from Cl to N. This conclusion is reinforced when the values of χ(35Cl) and χ(14N) predicted on the basis of a recent electrostatic hydrogen-bonded model (CH3)3N⋅⋅⋅HCl of the dimer are considered. The intermolecular stretching force constants kσ=84(3) N m−1 determined from DJ has a magnitude closer to that expected in the ion-pair limit than in the hydrogen-bond limit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456260
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  • 6
    Electronic Resource
    Electronic Resource
    Dissociation energies of the hydrogen-bonded dimers RCN⋅⋅⋅HF (R=CH3, HCC) determined by rotational spectroscopy (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2530-2535 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Measurements of absolute intensities of rotational transitions have been used to determine the zero-point and equilibrium dissociation energies D0 and De of the hydrogen-bonded dimers CH3CN⋅⋅⋅HF and HCCCN⋅⋅⋅HF. For CH3CN⋅⋅⋅HF reported values are D0=26.1(0.6) kJ mol−1 and De=29.0(0.9) kJ mol−1 while for HCCCN⋅⋅⋅HF the corresponding values are 20.4(0.7) and 23.4(0.9) kJ mol−1, respectively. The De values are used in conjunction with De=26.1(1.6) kJ mol−1 previously obtained for HCN⋅⋅⋅HF to investigate the suitability of the Morse and Lennard-Jones functions for describing the hydrogen-bond radial potential energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452106
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  • 7
    Electronic Resource
    Electronic Resource
    Microwave spectrum, structure, dipole moment, and deuterium nuclear quadrupole coupling constants of the acetylene–sulfur dioxide van der Waals complex (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6947-6955 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Thirty-three a- and c-dipole transitions of the acetylene–SO2 van der Waals complex have been observed by Fourier transform microwave spectroscopy and fit to rotational constants A=7176.804(2) MHz, B=2234.962(1) MHz, C=1796.160(1) MHz. The complex has Cs symmetry with the C2H2 and SO2 moieties both straddling an a–c symmetry plane (i.e., only the S atom lies in the plane). The two subunits are separated by a distance Rcm=3.430(1) A(ring) and the C2 axis of the SO2 is tilted 14.1(1)° from perpendicular to the Rcm vector, with the S atom closer to the C2H2. The dipole moment of the complex is 1.683(5) D. The deuterium nuclear quadrupole hyperfine structure was resolved for several transitions in both C2HD⋅SO2 and C2D2⋅SO2. A lower limit for the barrier to internal rotation of the C2H2 was estimated to be 150 cm−1 from the absence of tunneling splittings. The binding energy was estimated by the pseudo-diatomic model as 2.1 kcal/mol. A distributed multipole analysis was investigated to rationalize the structure and binding of the complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460228
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  • 8
    Electronic Resource
    Electronic Resource
    An investigation of hydrogen bonding between HCl and vinylacetylene: A molecule with two different π-acceptor sites (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6249-6255 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground state rotational spectrum of a hydrogen-bonded dimer formed by vinylacetylene and hydrogen chloride has been detected by the pulsed-nozzle, Fourier-transform microwave technique. Vinylacetylene has been chosen as a prototype acceptor molecule containing two different π-acceptor sites. Rotational constants A0, B0, C0, centrifugal distortion constants ΔJ, ΔJK, δJ, δK, and three components χaa, χbb−χcc, and χab of the Cl nuclear quadrupole coupling tensor have been determined for each of the three isotopomers CH2CHCCH⋅⋅⋅ H35Cl, CH2CHCCH⋅⋅⋅H37Cl, and CH2CHCCH⋅⋅⋅D35Cl. These spectroscopic constants have been interpreted in terms of a dimer in which the HCl subunit forms a hydrogen bond to the C 3/4 C triple bond in a T-shape configuration, but is displaced from the center of the triple bond by d=0.04 A(ring) towards the inner C atom, and makes an angle cursive-phi=34° with the vinylacetylene plane. The experimental angular geometry is in excellent agreement with that predicted by the Buckingham–Fowler electrostatic model which gives cursive-phi=27°.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458994
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  • 9
    Electronic Resource
    Electronic Resource
    Infrared diode-laser spectroscopy and Fourier-transform microwave spectroscopy of the (CO2,CO) dimer in a pulsed jet (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4440-4447 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two techniques have been used to observe the spectrum of a weakly bound dimer (CO2, CO) formed in a pulsed jet of CO2 and CO seeded in argon. The v=1←0 vibrational transition in the modified asymmetric stretching mode of the CO2 subunit was first observed at Doppler-limited resolution by investigating the pulsed jet with an infrared diode-laser spectrometer. Then the ground-state pure rotational spectrum was detected by applying Fourier-transform microwave spectroscopy to such a jet. A combined fit of the two spectra of the parent isotopomer gave the following set of ground-state (v=0) and excited-state (v=1) spectroscopic constants: A0=11 863.48(56) MHz, B0=1883.915(4) MHz, C0=1613.297(4) MHz, A1=11 772.17(37) MHz, B1=1882.76(6) MHz, C1=1611.44(5) MHz, ΔJ =8.145(2) kHz, ΔJK =339.42(1) kHz, δJ =1.26(1) kHz, and δK =309.8(4) kHz when the centrifugal distortion constants were constrained to be equal in both states. Spectroscopic constants for the isotopomers (CO2, 13CO) and (CO2, C18O) have also been determined. The nature of the observed spectra, especially the systematic absences of certain transitions, and the magnitudes of the spectroscopic constants have been interpreted in favor of a dimer with a T-shaped geometry in which the CO molecule lies along the C2 axis of CO2, with the two C atoms contiguous and r0(C⋅⋅⋅C)=3.277 A(ring). The intermolecular stretching force constant has the small value kσ =2.7 N m−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456780
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  • 10
    Electronic Resource
    Electronic Resource
    Rotational spectrum of a weakly bound dimer of formaldehyde and acetylene: Identification and characterization of a bridged planar form involving two nonlinear hydrogen bonds (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6793-6800 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Pulsed-nozzle, Fourier-transform microwave spectroscopy has been used to observe and measure the rotational spectra of the following five isotopomers of a weakly bound dimer formed between formaldehyde and acetylene: (H2CO,HCCH), (H2CO,DCCD), (H2CO,HCCD), (H2CO,DCCH), and (D2CO,HCCH). Rotational constants Av, Bv, Cv, and centrifugal distortion constants ΔJ, ΔJK, and δJ have been determined for the ground state (v=0) for all species and for a vibrationally excited state (v=1) for the first two. The values for the v=0 state in (H2CO,HCCH) are: A0=30 400.567(3) MHz, B0=2355.8304(3) MHz, C0=2180.3335(5) MHz, ΔJ =13.159(8) kHz, ΔJK =−311.4(2) kHz, and δJ =1.526(5) kHz. A detailed analysis of the rotational constants leads to the conclusion that the dimer has an unusual, bridged planar geometry, with the two subunits bound through two nonlinear hydrogen bonds. One bond has acetylene as the proton donor and the oxygen atom of formaldehyde as the acceptor while in the other a formaldehyde proton interacts with the acetylene π bond. The geometry is characterized by the following distances and angles: r=3.86(2) A(ring) is the distance from the C atom of H2CO to the center of C≡C, θ=80.3(16)° is the angle made by the C2 axis of H2CO with r while φ=40.1(17)° is the corresponding angle made by the acetylene axis. The hydrogen bond distances are r(O⋅⋅⋅H)=2.39 A(ring) and r(center⋅⋅⋅H)=3.12 A(ring). The vibrationally excited state has been identified with a motion involving the torsional oscillation of the H2CO subunit about its C2 axis. A relatively high barrier to this motion at 90° to the molecular plane is postulated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454425
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