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  • 1
    Electronic Resource
    Electronic Resource
    Rotational spectrum and structure of the hydrogen cyanide-carbon dioxide (CO2)2 trimer (1990)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 94 (1990), S. 7774-7780 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100383a007
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  • 2
    Electronic Resource
    Electronic Resource
    Tunneling in a linear B2H6–HCl dimer (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1552-1562 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotational spectra have been observed for eight isotopic species of the diborane–HCl complex with a Balle–Flygare, pulsed nozzle, Fourier transform microwave spectrometer. The dimer has a linear, or at most slightly bent B–B⋅⋅⋅H/DCl equilibrium structure with the H/D end of the HCl attracted symmetrically to a terminal BH2 group of the diborane. Three B2H6–HCl species homonuclear in the boron were observed to tunnel while those with 10B11BH6 or DCl did not. The tunneling splits each rotational transition into two components of comparable intensity, separated by several MHz depending on J and K. The a–dipole transitions are characteristic of a prolate, very near symmetric top; only K=0 and ±1 transitions were found. Rotational constants are reported for all species. The B¯, DJ, H, (B-C), and DJK constants determined for 11B2H6–H35Cl are for the A1 tunneling state 1273.364(1) MHz, 5.56(5) kHz, 1.0(8) Hz, 5.3(2) MHz, and −2.1(3) MHz; for the A2 tunneling state 1273.856(1) MHz, 11.64(7) kHz, 33.1(9) Hz, 5.70(4) MHz, and −3.21(5) MHz. The chlorine hyperfine structure gives the average torsional displacement of the H/DCl from the a axis to be 26.3° for the HCl complexes and 22.5° for the DCl. The torsional displacement of the B2H6 was found by an inertial analysis of the complexes with HCl. It is very anisotropic, being close to 0° in the ethylene plane and about 9° in the BH2B bridging plane. It is suggested that in the tunneling the B2H6 reorients by 180° in the bridging plane, coupled with a gear-like counter rotation of the HCl by 360°. The B⋅⋅⋅H distance is 2.693 A(ring) in the dimers with HCl and the B⋅⋅⋅D distance is slightly longer, 2.702 A(ring).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461070
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  • 3
    Electronic Resource
    Electronic Resource
    Rotational spectra and structures of small clusters containing the HCN dimer: X–(HCN)2 with X=CO, N2, NH3, and H2O (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6363-6370 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This work is the counterpart of a previous report on the (HCN)2–Y trimers with Y=HF, HCl, HCF3, and CO2 [J. Chem. Phys. 90, 4069 (1989)]. Rotational spectra have been observed for several isotopic species of the OC–, N2–, H3N–, and H2O–(HCN)2 trimers, using a pulsed nozzle, Fourier transform Balle/Flygare microwave spectrometer. The structures are basically composites of those reported for the (HCN)2 and X–HCN dimers. The trimers are effectively axially symmetric, but have some shrinkage of dimensions. Rotational constants found for the main isotopic species of each trimer are: For X=OC, a B0 of 421.142 MHz and DJ of 110 Hz; for X=N2, 435.573 MHz and 155 Hz; for X=H3N, a symmetric top, a B0 of 675.777 MHz, DJ of 180 Hz, and DJK of 41.1 kHz; and for X=H2O, with C2v symmetry, a (B0+C0)/2 of 667.028 MHz, (B0−C0)/2 of 0.617 MHz, DJ of 173 Hz, and a DJK of 62.9 kHz. The rotational constants for the isotopic species of each trimer were used to determine the distances r1 and r2 between the centers of mass (c.m.) of adjacent monomers, r1 being that for X–HCN and r2 that for (HCN)2. For X=OC, N2, H3N, and H2O the shrinkages found in r1 are 0.068, 0.056, 0.084, and 0.074 A(ring), respectively, and in r2 0.013, 0.013, 0.044, and 0.026 A(ring). The 14N quadrupole coupling constants were determined by selective 15N substitution for most of the nitrogen sites in the trimers. The effects of charge redistribution in the trimers were separated from those of torsional oscillations in several instances including N2 in N2–(HCN)2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458979
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  • 4
    Electronic Resource
    Electronic Resource
    Mutual polarization of monomer charge distribution in (HCN)2, (HCN)3, and (HCN)∞ (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2717-2722 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A simple classical mutual polarization model accurately predicts the induced dipole moments of linear HCN dimer and trimer. The model employs the first four nonzero electrical molecular moments of each HCN, and both the molecular polarizability and the C–H and C–N bond dipole polarizabilities. The model is extended to linear H-bonded oligomers up to the pentamer, and also to an infinite linear H-bonded chain, appropriate for comparison with the H-bonded chains present in the HCN crystal. For the dimer and trimer, a relation is seen between the change in the electric field gradient at the N of HCN and the calculated induced C–N bond dipole moment. A semiquantitative proportionality constant, derived based on this relation, is used to enhance understanding of the underlying cause of the large increase in the 14N quadrupole coupling constant in the HCN crystal relative to the free HCN monomer. This increase results from the strong polarization of the C–N bond by the local field at each HCN caused by the rest of the HCN crystal lattice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459847
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  • 5
    Electronic Resource
    Electronic Resource
    Rotational spectrum and structure of the HCN–(CO2)3 tetramer (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 862-869 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Microwave rotational transitions have been observed for HCN–(CO2)3, DCN–(CO2)3, H13CN–(CO2)3, HC15N–(CO2)3, HCN–(13CO2)3, HCN–(18OCO)(CO2)2, and HCN–(CO2)(C18O2)2 with the pulsed Fourier transform, Flygare/Balle Mark II spectrometer. A symmetric top spectrum was observed for the parent isotopic species with rotational constants of B0=861.6392(1) MHz, DJ =0.681(5) kHz, and DJK =0.821(12) kHz. The results for isotopic substitution indicate a zero-point, vibrationally averaged geometry having the C3 symmetry of a cyclic (CO2)3 structure with the HCN along the symmetry axis and the N end closest to the (CO2)3. The C3 symmetry is confirmed by the observation of states limited to K=±3n, with n=0,1,2,..., as predicted for threefold symmetry generated by bosons only. The (CO2)3 has a pinwheel configuration, as in the free trimer, and the three carbons lie in a plane R=2.758 A(ring) below the center of mass (c.m.) of the HCN. The C-C distance in this subunit is 3.797 A(ring) which is 0.241 A(ring) shorter than that found in the free (CO2)3 trimer. The individual CO2's in the (CO2)3 pinwheel are rotated out of the C–C–C plane by γ=−6.9°, as determined from an inertial analysis, with the inner oxygens rotated away from the HCN. The HCN has an average torsional angle of 10.3°, as determined by isotopic substitution, and an observed χcc value of −3.891 MHz for the 14 N. The c.m.(HCN) to C distance is 3.525 A(ring), compared to 3.592 A(ring) in the HCN-CO2 T-shaped dimer. The isotopic substitution by 18O perturbs the structure of the symmetric top clusters by a remarkable amount, decreasing γ to −28.9° and increasing R and RCC to 2.797 and 3.814 A(ring), respectively. In the 18O substituted species, the CO2's are rotated in the C–C–C plane from C3v symmetry by the pinwheel angle β=∼32.5°.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458118
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  • 6
    Electronic Resource
    Electronic Resource
    Rotational spectra and structures of small clusters containing the HCN dimer: (HCN)2–Y with Y=HF, HCl, HCF3, and CO2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4069-4078 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Microwave rotational spectra have been observed for a number of isotopic species of the (HCN)2–HF, –HCl, –HCF3, and –CO2 trimers. The observations were made with the pulsed nozzle, Fourier transform, Flygare/Balle Mark II spectrometer. The trimers have structures which are composites of the linear (HCN)2 dimer and the HCN–Y dimers, the latter linear for Y=HF and HCl, a symmetric top for Y=HCF3, and T-shaped with C2v symmetry for Y=CO2. The rotational constants for the most abundant species of each trimer are as follows: For Y=HF and HCl, B0 is 699.204 and 467.408 MHz, respectively, and DJ is 162 and 87 Hz; for Y=HCF3, B0 is 305.742 MHz and DJ and DJK are 51 and 471 Hz; for Y=CO2, treated as a symmetric top, (B0+C0)/2 is 452.426 MHz and DJ is 1.057 kHz. Hyperfine interaction constants were determined for several species. The B0's for each trimer were analyzed by a combination of isotopic substitution and fitting procedures to determine the distances r1 and r2 between the centers of mass (c.m.) of adjacent monomers. The B0's are relatively insensitive to the position of the central HCN but give r1+r2 accurately. With this limitation, r1 and r2 in the trimers are compared with the corresponding distances in the dimers, which are longer. For Y=HF, HCl, HCF3, and CO2, respectively, the shrinkages found in r1 are 0.069, 0.054, 0.030, and 0.004 A(ring) and in r2, 0.043, 0.062, 0.042, and 0.052 A(ring). The shrinkage in r1 and several other properties of the trimers exhibit some correlation with the pseudodiatomic stretching force constant in the HCN–Y dimer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456661
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  • 7
    Electronic Resource
    Electronic Resource
    Rotational spectrum and structure of the linear CO2–HCN dimer: Dependence of isomer formation on carrier gas (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4216-4221 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A linear hydrogen-bonded dimer, OCO–HCN, has been identified and characterized via its microwave rotational spectrum. The study was made using the pulsed nozzle Fourier transform method with the Flygare/Balle Mark II spectrometer. A T-shaped HCN–CO2 dimer was reported earlier by the Klemperer group. Rotational constants have been determined for all seven monoisotopically substituted species of the linear form. B0 , DJ , and χaa (14 N) for the normal isotopic dimer are 1057.9397(2) MHz, 1.372(8) kHz, and −4.2466(5) MHz, respectively. The average torsional displacements of the OCO and HCN monomers about their center of mass (c.m.) are found to be 7.66° and 12.40°, based on the substitution O–C and C–N bond distances for the dimer. With these values for α and γ, the B0 for the normal isotopic dimer corresponds to a c.m. to c.m. distance R=5.035 A(ring). Bending and stretching force constants and the well depth (ε∼590 cm−1 ) are estimated from the centrifugal distortion. The relative concentrations of the linear and T-shaped isomers are unusually sensitive to the carrier gas used in the supersonic jet expansion. The linear form could not be detected at all with argon as the carrier gas but gave a strong signal in neon first run (70% Ne, 30% He). In contrast, the T form gave strong signals in both carrier gases. However, a carrier-gas effect was not found for the N2 O/HF dimer pair, which has a high barrier between the bent NNO–HF and linear FH–NNO isomers. Similar results were obtained for chlorocyclohexane (CCH) and ethyl formate (EF), which have two conformational isomers. In CCH which has a high barrier to a↔e interconversion, the two conformers gave strong signals in both Ar and He. In EF, with a low barrier, the gauche conformer could not be detected in Ar but gave a strong signal in He, while the trans form gave strong signals in both carrier gases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455778
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  • 8
    Electronic Resource
    Electronic Resource
    Rovibrational state mixing in the aldehyde C–H stretch fundamental region of acetaldehyde (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3955-3961 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied rovibrational state mixing in acetaldehyde using infrared laser induced fluorescence. Molecules are isolated and cooled in supersonic molecular beams, and irradiated in the C–H stretch fundamental region with an infrared optical parametric oscillator. Spectral resolution is provided with either a circular variable filter machine or a cryogenic Michelson interferometer. We have found evidence of several strong Fermi resonances between the aldehyde C–H stretch and a few overtones and combinations of lower frequency modes. In addition, there is substantial random state mixing in this region as evidenced by the average experimental dilution factor of 0.2. The dependence of the dilution factor on the average J excited by the laser shows that the extent of state mixing scales linearly with J. We have observed from dispersed fluorescence spectra that random rotational coupling occurs between different Kp states. Our previous statistical coupling model has been applied to the interpretation of the data, and its applicability is discussed. For the model calculation, the methyl torsion is specially treated as a very anharmonic mode in the eumeration of the zeroth order bath states. The average coupling width derived from the model calculation is 0.35 cm−1. The relative energy content apportioned among vibrational modes in the molecule following excitation is measured and is successfully explained with the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455705
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  • 9
    Electronic Resource
    Electronic Resource
    Rotational spectra, dipole moment, and structure of the SiF4–NH3 dimer (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3441-3446 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotational spectra of several isotopic species of the SiF4–NH3 dimer were obtained with the Mark II Flygare–Balle FT-MW spectrometer. This is the first determination of the gas phase structure of a penta-coordinated silicon. The spectra indicate a symmetric top, trigonal bipyramid SiF3N structure with the lone electron pair of the NH3 pointed at one face of the SiF4 and the three equatorial F's splayed significantly away from the N. The (angle)Fax–Si–Feq is about 12° less than tetrahedral. The Si–N distance is determined to be 2.090 A(ring). The experimental results are in excellent agreement with the SiF4 deformation predicted by the ab initio calculations of Rossi and Jasinski [Chem. Phys. Lett. 169, 399 (1990)]. The measured dipole moment is 5.61 D, an enormous enhancement compared to the sum of the monomer moments, 1.47 D. The increase of 4.14 D is due largely to the geometric distortion of the tetrahedral SiF4 molecule upon dimer formation, demonstrating that the Si–F bond is much more ionic than covalent. If the charge is simply partitioned between Si and F so as to obtain a moment of 4.14 D, the Si has a charge of +3.52 and each F, −0.88. This conclusion is consistent with recent applications of the atoms-in-molecules charge partition methodology developed by Bader and co-workers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461947
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  • 10
    Electronic Resource
    Electronic Resource
    Relaxation of conformers and isomers in seeded supersonic jets of inert gases (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 3142-3150 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied the relaxation of conformers and the formation/relaxation of isomeric, weakly bonded dimers in pulsed supersonic expansions of seeded inert gases (He, Ne, Ar, Kr). The relaxation was determined from the intensity of a rotational transition for the higher energy species as a function of carrier gas composition, using the Balle/Flygare Fourier transform microwave spectrometer. Of thirteen molecules with rotational conformers which we examined, those with barriers to internal rotation greater than 400 cm−1 did not relax significantly in any of the carriers. The higher energy forms of ethyl formate, ethanol, and isopropanol, with smaller barriers, were not relaxed by He; those of ethanol and isopropanol were somewhat relaxed by Ne; and all were completely relaxed by as little as 5 to 20 mole percent of Ar or Kr in He or Ne. The relaxation in He or Ne is first order in the concentration of added Ne, Ar, or Kr as well as in the concentration of the high energy conformer. The pseudo first-order rate constants (larger in Ne than in He) increase sharply with Z of the rare gas, roughly in a 0:1:2:4 progression for He, Ne, Ar, and Kr, suggesting that the relaxation involves relatively long-range polarization effects. Similar behavior was found in the formation/relaxation of the weakly bonded dimer pairs: linear OCO–HCN, T-shaped HCN–CO2; linear FH–NNO and bent NNO–HF; and bent HF–DF and DF–HF. The case of the HCN/CO2 dimers is particularly striking. The T-shaped dimer was found first, using Ar as the carrier gas. Five years later the linear form was found with first run neon as carrier, but it could not be detected at all with Ar as the carrier. These results show that in favorable cases high energy species can be studied in supersonic expansions by freezing out a "high-temperature'' concentration with a nonrelaxing carrier gas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458848
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