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  • 1
    Online Resource
    Online Resource
    Advanced Theories and Computational Approaches to the Electronic Structure of Molecules. (1984)
    Dordrecht :Springer Netherlands,
    Details
    Keywords: Molecular structure-Congresses. ; Electronic structure-Congresses. ; Electronic books.
    Description / Table of Contents: Proceedings of the NATO Advanced Research Workshop on Vectorization of Advanced Methods for Molecular Electronic Structure, Colorado Springs, Colorado, U.S.A., September 25-29, 1983.
    Type of Medium: Online Resource
    Pages: 1 online resource (241 pages)
    Edition: 1st ed.
    ISBN: 9789400964518
    Series Statement: Nato Science Series C: Series ; v.133
    URL: https://ebookcentral.proquest.com/lib/geomar/detail.action?docID=6558714
    Language: English
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    Structure and dynamics of the H2O–HCN dimer (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 5808-5816 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This report extends an earlier microwave study of the H2O –HCN weakly bonded dimer by Legon [Proc. R. Soc. London, Ser. A 396, 405 (1984)]. We have resolved the H–H(H2O) hyperfine structure (hfs) in rotational transitions of H2O–HC15N and the 17O hfs in H217O–HC15N, using a modified Balle/Flygare Fourier transform microwave spectrometer with a pulsed supersonic nozzle as the sample source. Also, the rotational constants of H2O–H13CN have been determined. The hfs, particularly that of 17O, and a substitution analysis, are used to clarify the dynamics of the dimer. The analyses support a pseudoplanar, H2O –HCN, C2v structure in which the H2O and HCN experience in-plane and out-of-plane bending vibrations of modest on average amplitude. The out-of-plane H2O bend is 20° and the in-plane is perhaps half that. The bending of the HCN is isotropic, with an amplitude of 9.4° in both directions. The molecular mechanics for clusters (MMC) model was used to explore the potential energy surface (PES) for the weak-bonding coordinates. The calculated equilibrium structure differs greatly from the experimental, with the H2O rotated out of plane by 60° in one direction and the HCN by 20° in the other (cis). The difference is shown by the 17O hfs and its dependence upon the H2O bending to be caused by the zero-point vibrational averaging of the structure, which extends over the shallow symmetric double minimum in the PES. The interaction energy is large (−1590 cm−1 ), but the PES is relatively flat in the bending coordinates over large regions between the equilibrium minima, making the vibrational averages differ substantially from the equilibrium values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462680
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  • 4
    Electronic Resource
    Electronic Resource
    J dependence of χa(14N) for the Ar–HCN dimer: Coupling of stretching and bending in the potential function (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 30-38 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The previously reported rotational spectrum of Ar–HCN [J. Chem. Phys. 81, 4922 (1984)] has shown the weakly bound dimer to be highly nonrigid. Superficially linear, the dimer has several anomalies, including large centrifugal distortion and an unexpectedly large bending amplitude of the HCN. We here describe high-resolution rotational spectra which identify another anomaly. The 14N hyperfine interaction constant of the dimer increases linearly with J(J+1) for Ar–HCN, 36Ar–HCN, and Ar–DCN, indicating a decrease in the average HCN bending amplitude (θ). For Ar–HCN this is from 30.97° for J=0 to 30.17° for J=5. At the same time, there is an increase in the average Ar to HCN c.m. separation R from 4.3433 to 4.3496 A(ring). The cause of this behavior and of the other anomalies is found to be the shape of the potential function as calculated with a largely classical electrical model employing low-order moments and multipole polarizabilities. The calculated potential surface exhibits strong coupling between radial and angular motions, with smaller angles favored at larger R. There is an axial hump in the potential curve generated by rotating the HCN through the linear structure, and the height of the hump is sensitive to R. In contrast, a hump is not found in the equilibrium region of the potential surface for Ar–HF. The difference between the two surfaces arises from the combination of their similar electrical interactions with different hard-wall effects. Basically, the differences in the shapes of HF (nearly spherical) and HCN (cigar shaped) give interaction surfaces that cause the properties of Ar–HCN to contrast with those of Ar–HF. An important part of the constrast is the fact that the hydrogen halides are unusual in being more spherical than most other highly polar molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456531
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  • 5
    Electronic Resource
    Electronic Resource
    Rotational spectrum and structure of the Ne–HCN dimer (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 6801-6809 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Microwave rotational transitions have been observed at low J (0–3) for several isotopic species of the Ne–HCN dimer using the Balle/Flygare Mark II Fourier transform spectrometer with a pulsed nozzle as the source. For 20Ne–HC 14N, the main K=0 transitions give rotational constants B¯, DJ, and HJ of 2772.816 and 1.280 MHz and 1.173 kHz. The 14N nuclear quadrupole constant increases linearly with J(J+1) at a slope Dχ of −12.7 kHz from a value for χa(14N) of −0.957 MHz at J=0. The pseudodiatomic approximation for B¯ and χa(14N) leads to a value of 3.89 A(ring) for the Ne to HC 14N center-of-mass (c.m.) distance R, and to 46.8° for the "average'' bend angle θ of HC 14N. Some of the K=0, J=1→2, and J=2→3 transitions exhibit one or two weak satellites ∼30 MHz away, usually below, but also both above and below. The J=1→2 low frequency satellites for 20Ne–HC 14N and 20Ne–HC 15N, nominally 111→212, are symmetrical doublets with splittings of 305 and 439 kHz, respectively. The 14N hyperfine structure (hfs) is identical for the two 20Ne–HC 14N components as is the Stark effect for 20Ne–HC 15N. The molecular mechanics for clusters (MMC) model was used to calculate potential energy surfaces for Rg–HCN dimers, giving stabilities of 21, 37, 85, and 108 cm−1 with He, Ne, Ar, and Kr as the rare gas. A qualitative comparison of the experimental properties for the dimers with Ne, Ar, and Kr as the rare gas is based on the surfaces. The extremely mobile internal dynamics of Ne–HCN are attributed to its potential surface, which is both very shallow and isotropic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464771
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  • 6
    Electronic Resource
    Electronic Resource
    Rotational spectrum and structure of an (H2O–HCN)–Ar trimer (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3032-3040 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotational transitions of the (H2O–HCN)–Ar trimer have been measured at 3–17 GHz with the Balle/Flygare Mark II pulsed nozzle FT microwave spectrometer for the parent, 18O, 13C, 15N, D2O, and HDO isotopic species. The isotopomers exhibit both a- and b-dipole transitions with 14N hyperfine structure and all but the HDO have two sets of transitions assigned to 000 and 101 internal rotational states of the H2O or D2O. Rotational constants were determined by fitting the line centers separately for each isotopic set to the Watson Hamiltonian for an asymmetric top. A molecular mechanics for clusters (MMC) calculation of the potential energy surface and an approximate substitution analysis of the rotational constants give a nearly planar, Δ-shaped structure which is a somewhat distorted superposition of the H2O–HCN, H2O–Ar, and Ar–HCN dimers. MMC also gives a barrier of (approximately-less-than)25 cm−1 to internal rotation of the H2O. Factors governing the formation of trimers are discussed. The effects on trimer structure of differences in the pair interactions are found to be appreciable while the role of three-body effects is small. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468613
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  • 7
    Electronic Resource
    Electronic Resource
    Rotational spectra and structures of the C6H6–HCN dimer and Ar3–HCN tetramer (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 3917-3927 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A comparative study has been made of the rotational properties of C6H6–HCN and Ar3–HCN, observed with the Balle/Flygare pulsed beam, Fourier transform microwave spectrometer. C6H6–HCN is found to be a prolate symmetric top and Ar3–HCN an oblate one, both with the H in the middle. The rotational constants B0, DJ, and DJK of the parent species are 1219.9108(4) MHz, 1.12(3) kHz, and 18.32(8) kHz for C6H6–HCN, and 886.4878(1) MHz, 10.374(2) kHz, and 173.16(1) kHz for Ar3–HCN. Rotational constants are reported for the isotopic species C6H6–H13CN, -HC15N, and 13CC5H6–HC15N, and for Ar3–HC15N and -DCN. Analysis of the 14N hyperfine interaction χ finds its projection on the figure axis to be −4.223(4) MHz in C6H6–HCN and −1.143(2) in Ar3–HCN. They correspond to average projection angles θ between the HCN and figure axes of 15.2° and 45.3°, respectively. A pseudodiatomic analysis of the rotational constants gives the c.m. to c.m. distance to be 3.96 A(ring) in C6H6–HCN and 3.47 A(ring) in Ar3–HCN. While the rotational properties of C6H6–HCN are "normal,'' those of Ar3–HCN display a long list of "abnormalities.''They include a J-dependent χ(14N) similar to that of Ar–HCN; a very large projection angle θ; large centrifugal distortion including higher-order terms in HJ and HJK; splitting of the K=3 transitions into J-dependent doublets; and the ready observation of an excited vibrational state. These behavioral differences are related qualitatively to the interaction surfaces for the two clusters, calculated with the molecular mechanics for clusters (MMC) model, and discussed. The potential minimum for C6H6–HCN is smooth, circular, steep except for a flat bottom, and deep (1762 cm−1). That for Ar3–HCN is tricuspid, with large gullies, and shallow (507 cm−1). In addition to the dispersion forces, the dominant interaction forming C6H6–HCN is between the benzene quadrupole moment and the HCN dipole moment, a strong 4-2 potential. That in Ar3–HCN is polarization of the spherical Ar by the HCN dipole and quadrupole moments, a weak 0–2,4 potential. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469579
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  • 8
    Electronic Resource
    Electronic Resource
    Rotational spectra, structures, and dynamics of small Arm–(H2O)n clusters: The Ar2–H2O trimer (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 8495-8501 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotational spectra have been observed for the Ar2–H2O trimer and several of its isotopomers with the Balle/Flygare pulsed nozzle, Fourier transform microwave spectrometer. Analysis gives a planar T-shaped structure with C2v symmetry and the bidentate protons pointed at the argons. Two sets of asymmetric top transitions were found for the species with H2O, D2O, or H2 18O. Several lines of evidence support assigning them to internal rotor states of the water, the upper set to Σ(000) and the lower to Σ(101) as in the Ar–H2O dimer. Support includes: Hyperfine interaction constants which differ for the two states of water; Systematic aspects of the rotational constants such as B's that are little affected by isotopic substitution; and MMC calculations which indicate the importance of rovibrational coupling. The Ar–Ar distance for the Σ(000) state of the trimer is estimated to be 3.822 A(ring) and the center of mass (Ar2) to center of mass (H2O) distance to be 3.173 A(ring). An intriguing result is finding the hyperfine interaction constants of the water in the trimer to be very nearly the same as those reported earlier for the dimer. This shows the two dynamic states of the water are the same in the dimer and trimer, as is the average projection of the water C2 axis onto the inertial frame. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472611
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  • 9
    Electronic Resource
    Electronic Resource
    Local Quantum Chemistry (1990)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physical Chemistry 41 (1990), S. 155-174 
    Details
    ISSN: 0066-426X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.pc.41.100190.001103
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  • 10
    Electronic Resource
    Electronic Resource
    Potential Energy Barriers in Unimolecular Rearrangements (1981)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physical Chemistry 32 (1981), S. 25-52 
    Details
    ISSN: 0066-426X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.pc.32.100181.000325
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