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  • 1
    Electronic Resource
    Electronic Resource
    Microwave spectrum, dipole moment, and dynamic structure of the "linear'' HCCH–CO dimer (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 1619-1623 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotational spectra have been observed for several 13C/18O isotopic species of the pseudolinear acetylene–carbon monoxide dimer using the pulsed, Fourier transform Balle/Flygare microwave spectrometer. A quadrature detection system has been incorporated in the data processing system to avoid folding of the spectrum onto itself in taking the Fourier transform. Dipole moments of 0.3112(12) and 3.29(3) D were determined for the parent HCCH–CO species and for HCN–HCCH, respectively. Structural properties were derived from the various measurements, including a well depth of 300 cm−1 from DJ, and the results are compared with those reported earlier for HCN–HCCH. A substitution analysis is developed in which the rotational properties of a pseudolinear dimer are treated as a symmetric top. A simple method is described for determining effects of the off-axis bending of the monomers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463203
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  • 2
    Electronic Resource
    Electronic Resource
    Kinetics of molecular association and relaxation in a pulsed supersonic expansion (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8830-8839 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The formation of polar Ar/HCN dimers and trimers in supersonic jets has been studied by observing the intensity of rotational transitions in the expanded pulsed jet as a function of input gas composition at a backing pressure of 1 to 2 atm. A programmable gas flow system was employed for accurate control of the composition of the gas mixture supplied to the pulsed nozzle. The formation of Ar–HCN was found to be first order in [Ar] and in [HCN]; (HCN)2 to be second order in [HCN]; (HCN)3 to be second order in [HCN]; and both Ar2–HCN and (HCN)2–Ar to be first order in [Ar] and in [HCN]. The three trimers are formed in two consecutive bimolecular steps at steady state, with (HCN)2 as the intermediate for (HCN)3, and Ar–HCN as the intermediate for both Ar2–HCN and (HCN)2–Ar. Less extensive measurements were made on the HCN/CO2 system, in which formation of the T-shaped HCN–CO2 dimer was found to be first order in [HCN] and in [CO2]. The rare gases He, first-run Ne (70% Ne, 30% He), and Ar were used as carrier gases. The carrier gas plays a major role as a third body in the formation steps. The relative effectiveness of the carrier gases as a relaxant in forming the dimers and trimers is Ar〉Ne (first run)(very-much-greater-than)He. The method and results are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462240
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  • 3
    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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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    J dependence of χa(14N) and χa(83Kr) for the Kr–HCN dimer (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 6302-6308 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-resolution microwave rotational spectra for 84Kr–HCN, 86Kr–HCN, and 83Kr–HC15N have been observed with the pulsed-nozzle, Fourier transform Balle/Flygare Mark II spectrometer. A new method of injecting the gas sample into the Fabry–Perot cavity along the axis of the microwave pulse was used for some transitions to narrow the linewidths. The present work extends that of the original study [J. Chem. Phys. 78, 3483 (1983)] over a wider frequency range (2–18 GHz) and with higher resolution. The 14N nuclear quadrupole coupling constant has been found to increase linearly with J(J+1) for 84Kr–HCN and 86Kr–HCN, with the slope Dχ one-third its value for the analogous Ar–HCN dimer. For 84Kr–HCN, the average HCN bending amplitude θ decreases from 26.85° for J=0 to 26.28° for J=7, while the average Kr to HCN center-of-mass (c.m.) distance R increases from 4.5202 to 4.5246 A(ring). Similar results are found for 86Kr–HCN. In addition, the 83Kr quadrupole coupling constant for 83Kr–HC15N is dependent on J, increasing from 7.5382 MHz for J=1 to 7.5713 MHz for J=4. This is interpreted with the long-range polarization model used previously to explain rare gas nuclear quadrupole coupling constants in Rg–HX dimers. In particular, the J dependence observed for χa(83Kr) is consistent with the J dependencies of θ and R inferred from χa(14N) in the 14N species. Radial and angular motions of HCN are strongly coupled.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461550
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  • 6
    Electronic Resource
    Electronic Resource
    Rotational spectra of Ar2–DCl and Ar3–DCl, and a pseudotriatomic force field for Ar2–H/DX (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 63-68 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Microwave rotational transitions have been observed for Ar2–D35Cl and Ar3–D35Cl/37Cl. The Cl and D hyperfine interactions have been analyzed and rotational constants determined. The structures of the clusters are similar to those reported earlier for Ar2–HF/Cl and Ar3–HF/Cl. Ar2–D35Cl is a T-shaped asymmetric top with the DCl along the C2v axis. The A, B, and C rotational constants are 1735.0958(5), 1651.6749(8), and 840.5459(1) MHz, respectively. The four independent centrifugal distortion constants, τaaaa, τbbbb, τaabb, and τabab, are −0.1171(3), −0.0763(2), 0.037 64, and −0.060 88 MHz. The 35Cl quadrupole interaction is anisotropic and slightly J dependent, with a χaa of −38.184 0(7) and (1/(6)1/2)(χbb−χcc) of −1.3380 MHz for the 101→202 transition. χaa(D) was found to be 111.4 kHz. Ar3–DCl is a symmetric top with the DCl along the C3v axis. B0, DJ, DJK, χaa(35Cl), and χaa (D) for Ar3–D35Cl are 840.2264 MHz, 2.268 and 1.921 kHz, and −39.717(3) and 0.128(4) MHz, respectively. Analysis of the change in B0 with 35Cl/37Cl substitution shows conclusively that the DCl is oriented with the D end closest to the argons. A pseudotriatomic, bent XY2 model is used with the centrifugal distortion constants of Ar2–H/DF and –H/DCl to predict force constants, vibrational frequencies, and inertial defects of the four clusters. The predicted Ar–Ar stretching frequency of 21.8 to 23.0 cm−1 in the clusters compares favorably with the 25.7 cm−1 experimental value reported for free Ar2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457449
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  • 7
    Electronic Resource
    Electronic Resource
    Rotational spectra, structure, Kr-83 nuclear quadrupole coupling constant, and the dipole moment of the Kr-benzene dimer (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5335-5340 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotational spectra were observed for the Kr-82, Kr-83, Kr-84, and Kr-86 isotopic species of the Kr-benzene dimer with the Mark II Balle-Flygare Fourier transform microwave spectrometer. The spectra are those of a symmetric top, with the Kr on the symmetry axis of the benzene. In the most abundant Kr-84 benzene dimer the rotational constants B0, DJ, and DJK were found to be 795.6821(1) MHz, 1.315(1) kHz, and 7.895(4) kHz, respectively. R, the Kr to benzene center-of-mass distance, is 3.663 A(ring) and the zero-point vibrational bending of the benzene with respect to R gives an average angular displacement of 16.6°. The Kr-83 quadrupole coupling constant was determined experimentally to be −5.201(5) MHz and the dipole moment, 0.136(2) D. A theoretical prediction of these electrically induced properties gives results for a distributed multipole model which are superior to those using central multipoles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463793
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  • 8
    Electronic Resource
    Electronic Resource
    Rotational spectra of the ∑ bend states of Ar–H/DCl and the ∑ stretch of Ar–HCl (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 86-91 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotational transitions of excited van der Waals states of Ar–H/DCl have been observed using the Balle–Flygare pulsed nozzle, Fourier transform, microwave spectrometer. Rotational constants and hyperfine interactions have been determined for the 35Cl/37Cl isotopes of both Ar–HCl and Ar–DCl in the lowest ∑ bending state. The HCl results are in good agreement with previous tunable far-infrared work [J. Chem. Phys. 89, 1268 (1988)]. For Ar–D35Cl and Ar–D37Cl, the rotational constants B and D and the quadrupole interaction χaa(Cl) were determined to be 1727.9887(1) MHz, 39.505(1) kHz, and −28.246(9) MHz, respectively, and 1686.4892(2) MHz, 39.167(4) kHz, and −22.344(10) MHz. χaa(D) for the Ar–D35Cl was found to be 132(7) kHz. Analysis of the 35Cl/37Cl isotope effects shows that the H(D) in H(D)Cl is pointed predominately away from the Ar. Measurement of the J=0→1 to J=4→5 transitions and their hyperfine structure for the ∑-stretch state of Ar–H35Cl give the rotational constants B, D, H, L, and the quadrupole interaction χaa(Cl) to be 1562.876(1) MHz, −67.2(1) kHz, −415(7) Hz, 1.6(1) Hz, and −20.774(7) MHz, respectively. The negative D centrifugal distortion constant and the large H and L constants suggest that this state is strongly perturbed by Coriolis interaction with the π bending state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460311
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  • 9
    Electronic Resource
    Electronic Resource
    Rotational spectrum and potential surface for Ar2–HCN: A T-shaped cluster with internal rotation (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6216-6225 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational spectrum of Ar2–HCN has been observed between 2.5 and 11.5 GHz with the pulsed nozzle, Fourier transform, Balle/Flygare Mark II microwave spectrometer. Eighteen transitions were found and their 14N quadrupole hyperfine structure analyzed. The line centers were fitted with the Watson Hamiltonian giving ground state rotational constants of 1769.366, 1743.854, and 857.600 MHz. The effective geometry of the cluster is found to be T-shaped with C2v symmetry and the H end of the HCN closest to the Ar2. However, the rms deviation of the fit is poor (300 kHz), the centrifugal distortion and inertial defect are huge, the Ar to HCN c.m. distance is nearly 0.2 A(ring) shorter than in the Ar–HCN dimer, and the average angular displacement of the HCN from the C2 axis is both large (39°) and highly anisotropic (10°). In contrast, the Ar2 subunit exhibits an in-plane, average angular displacement of only 6°. These anomalies led us to calculate potential surfaces for Ar2–HCN and Ar2–HF using the molecular mechanics for clusters scheme. A comparison of the surfaces and the rotational properties of the two species prompts us to propose that in Ar2–HCN the HCN axis rotates about the C2 axis maintaining an angle of ∼40° between them for the m=0 internal rotation state. Such internal rotation accounts at least qualitatively for the otherwise anomalous rotational behavior of the Ar2–HCN cluster.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458991
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  • 10
    Electronic Resource
    Electronic Resource
    Structure of the H2O–(CO2)2 trimer (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 894-896 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotational constants reported previously [J. Chem. Phys. 90, 5964 (1989)] for the C2 asymmetric tops H2O–(CO2)2, D2O–(CO2)2, H218O–(CO2)2 and H2O–(13CO2)2 have been reanalyzed. It is found that the slipped parallel (CO2)2 subunit, instead of remaining planar as in the free dimer, has the inner oxygens rotated away from the H2O by ∼20°. This leads to C–C and c.m. (H2O) to c.m. (CO2)2 distances of 3.497 and 2.370 A(ring) in the clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459115
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