@article {2623,
title = {Stretch-bend combination polyads in the (A)over-tilde(1)A(u) state of acetylene, C2H2},
journal = {Journal of Molecular Spectroscopy},
volume = {256},
number = {2},
year = {2009},
note = {ISI Document Delivery No.: 478PDTimes Cited: 0Cited Reference Count: 55Steeves, Adam H. Bechtel, Hans A. Merer, Anthony J. Yamakita, Nami Tsuchiya, Soji Field, Robert W.},
month = {Aug},
pages = {256-278},
type = {Article},
abstract = {Rotational analyses are reported for a number of newly-discovered vibrational levels of the SI-trans; ((A) over tilde (1)A(u)) state of C2H2. These levels are combinations where the Franck-Condon active nu(2){\textquoteright} and nu(3){\textquoteright} vibrational modes are excited together with the low-lying bending vibrations, nu(4){\textquoteright} and nu(6){\textquoteright}. The structures of the bands are complicated by strong a- and b-axis Coriolis coupling, as well as Darling-Dennison resonance for those bands that involve overtones of the bending vibrations. The most interesting result is the strong anharmonicity in the combinations of nu(3){\textquoteright} (trans bend, a(g)) and nu(6){\textquoteright} (in-plane cis bend, b(u)). This anharmonicity presumably represents the approach of the molecule to the trans-cis isomerization barrier, where ab initio results have predicted the transition state to be half-linear, corresponding to simultaneous excitation of nu(3){\textquoteright} and nu(6){\textquoteright}. The anharmonicity also causes difficulty in the least squares fitting of some of the polyads, because the simple model of Coriolis coupling and Darling-Dennison resonance starts to break down. The effective Darling-Dennison parameter, K-4466, is found to increase rapidly with excitation of nu(3){\textquoteright}, while many small centrifugal distortion terms have had to be included in the least squares fits in order to reproduce the rotational structure correctly. Fermi resonances become important where the K-structures of different polyads overlap, as happens with the 2(1)3(1)B(1) and 3(1)B(3) polyads (B = 4 or 6). The aim of this work is to establish the detailed vibrational level structure of the S-1-trans state in order to search for possible S-1-cis ((1)A(2)) levels. This work, along with results from other workers, identifies at least one K sub-level of every single vibrational level expected up to a vibrational energy of 3500 cm(-1). (C) 2009 Elsevier Inc. All rights reserved.},
keywords = {1AU, AB-INITIO MO, acetylene, Cis-trans isomerization, DISPERSED, DOUBLE-RESONANCE SPECTROSCOPY, FLUORESCENCE, FLUORESCENCE-SPECTRUM, INTRAMOLECULAR VIBRATIONAL REDISTRIBUTION, LASER-INDUCED, PARTIAL DEPERTURBATION, POLYATOMIC-MOLECULES, ROTATION CONSTANTS, STATE, vibration-rotation analysis, X BAND SYSTEM},
isbn = {0022-2852},
url = {://000268599300013},
author = {Steeves, A. H. and Bechtel, H. A. and Merer, A. J. and Yamakita, N. and Tsuchiya, S. and Field, R. W.}
}
@article {2186,
title = {Darling-Dennison resonance and Coriolis coupling in the bending overtones of the (A)over-tilde (1)A(u) state of acetylene, C2H2},
journal = {Journal of Chemical Physics},
volume = {129},
number = {5},
year = {2008},
note = {ISI Document Delivery No.: 336AGTimes Cited: 3Cited Reference Count: 57Merer, Anthony J. Yamakita, Nami Tsuchiya, Soji Steeves, Adam H. Bechtel, Hans A. Field, Robert W.},
month = {Aug},
pages = {19},
type = {Article},
abstract = {Rotational analyses have been carried out for the overtones of the nu(4) (torsion) and nu(6) (in-plane cis-bend) vibrations of the (A) over tilde (1)A(u) state of C2H2. The v(4)+v(6)=2 vibrational polyad was observed in high-sensitivity one-photon laser-induced fluorescence spectra and the v(4)+v(6)=3 polyad was observed in IR-UV double resonance spectra via the ground state nu(3) (Sigma(+)(u)) and nu(3)+nu(4) (Pi(u)) vibrational levels. The structures of these polyads are dominated by the effects of vibrational angular momentum: Vibrational levels of different symmetry interact via strong a-and b-axis Coriolis coupling, while levels of the same symmetry interact via Darling-Dennison resonance, where the interaction parameter has the exceptionally large value K-4466=-51.68 cm(-1). The K-structures of the polyads bear almost no resemblance to the normal asymmetric top patterns, and many local avoided crossings occur between close-lying levels with nominal K-values differing by one or more units. Least squares analysis shows that the coupling parameters change only slightly with vibrational excitation, which has allowed successful predictions of the structures of the higher polyads: A number of weak bands from the v(4)+v(6)=4 and 5 polyads have been identified unambiguously. The state discovered by Scherer [J. Chem. Phys. 85, 6315 (1986)], which appears to interact with the K=1 levels of the 3(3) vibrational state at low J, is identified as the second highest of the five K=1 members of the v(4)+v(6)=4 polyad. After allowing for the Darling-Dennison resonance, the zero-order bending structure can be represented by omega(4)=764.71, omega(6)=772.50, x(44)=0.19, x(66)=-4.23, and x(46)=11.39 cm(-1). The parameters x(46) and K-4466 are both sums of contributions from the vibrational angular momentum and from the anharmonic force field. For x(46) these contributions are 14.12 and -2.73 cm(-1), respectively, while the corresponding values for K-4466 are -28.24 and -23.44 cm(-1). It is remarkable how severely the coupling of nu(4) and nu(6) distorts the overtone polyads, and also how in this case the effects of vibrational angular momentum outweigh those of anharmonicity in causing the distortion. (C) 2008 American Institute of Physics.},
keywords = {ANHARMONIC-OSCILLATOR MODEL, DISPERSED, ELECTRONIC-TRANSITION, EXCITED-STATES, FLUORESCENCE-SPECTRUM, INTRAMOLECULAR VIBRATIONAL REDISTRIBUTION, PARTIAL DEPERTURBATION, POLYATOMIC-MOLECULES, ROTATION CONSTANTS, TRIPLET PERTURBATIONS, X BAND SYSTEM},
isbn = {0021-9606},
url = {://000258336100016},
author = {Merer, A. J. and Yamakita, N. and Tsuchiya, S. and Steeves, A. H. and Bechtel, H. A. and Field, R. W.}
}
@article {1069,
title = {Molecules with large-amplitude torsional motion partially oriented in a nematic liquid crystal: Ethane and isotopomers},
journal = {Journal of Physical Chemistry A},
volume = {109},
number = {48},
year = {2005},
note = {ISI Document Delivery No.: 990RPTimes Cited: 10Cited Reference Count: 48},
month = {Dec},
pages = {11027-11036},
type = {Article},
abstract = {An NMR study on ethane and five isotopomers dissolved in the nematic liquid crystal Merck ZLI 1132 is performed. A consistent set of dipolar and quadrupolar couplings is obtained. The dipolar couplings are corrected for harmonic vibrational effects, while the contribution from the torsional motion is incorporated classically. The corrected dipolar couplings cannot be understood in terms of a reasonable molecular structure unless effects of the reorientation-vibration interaction are taken into account. Assuming that the reorientation-vibration contributions that are known for the methyl group in methyl fluoride are transferable to ethane, excellent agreement between observed and calculated dipolar couplings is obtained on the basis of the ethane gas-phase structure. The observed and calculated deuterium quadrupolar couplings show discrepancies supporting the notion that average electric field gradients are important in liquid-crystal solvents. An important consequence of the transferability of the reorientation-vibration correlation is that in other molecules with a methyl group the same procedure as for ethane can be followed. Inclusion of this effect generally removes the need to interpret changes in observed dipolar couplings in terms of elusive chemical effects.},
keywords = {ANISOTROPIC, ELECTRIC-FIELD GRADIENTS, ENVIRONMENTS, FORCE-FIELDS, H-2 NMR, NUCLEAR-MAGNETIC-RESONANCE, orientational order, POLYATOMIC-MOLECULES, ROTATION, SPECTRA, VIBRATIONS},
isbn = {1089-5639},
url = {://000233761200026},
author = {Burnell, E. E. and de Lange, C. A. and Barnhoorn, J. B. S. and Aben, I. and Levelt, P. F.}
}
@article {4371,
title = {The forbidden rotational Q-branch of CH3CF3: Torsional properties and (A(1)-A(2)) splittings},
journal = {Journal of Molecular Spectroscopy},
volume = {190},
number = {2},
year = {1998},
note = {ISI Document Delivery No.: 103JBTimes Cited: 8Cited Reference Count: 29},
month = {Aug},
pages = {324-340},
type = {Article},
abstract = {The pure rotational spectrum driven by the small distortion dipole moment perpendicular to the symmetry axis has been investigated between 8 and 18 GHz for CH3CF3 in the ground vibrational state using a pulsed Fourier transform waveguide spectrometer. This molecule has been selected as a prototype for the case of a symmetric top with small (similar to 500 kHz) torsional energy splittings in the ground torsional state (v(6) = 0). In this state, six (k +/- 3 <{\textendash} k) e-branch series have been measured for lower state K = \k\ between 3 and 8 with 27 less than or equal to J less than or equal to 75, For (v(6) = 1), three series with lower state K between 5 and 7 with 49 less than or equal to J less than or equal to 66 have been observed. In two of these series, the torsional fine structure extending over similar to 6.8 MHz has been fully resolved. The (A(1) - A(2)) splitting has been measured in the (v(6) = 0) series (K = 6 <{\textendash} 3) for 37 less than or equal to J less than or equal to 74. The global data set of 443 frequencies included avoided-crossing molecular-beam splittings of Meerts and Ozier (1991. Chem. Phys. 152, 241-259) and mm-wave R-branch measurements of Bocquet et nl. (1994. J, Mol. Spectrosc. 165, 494-499). In a weighted least-squares analysis, a good fit was obtained by varying 18 parameters in a Hamiltonian that represented both the torsional effects and the sextic splittings. Effective values have been determined for both rotational constants, eight torsional parameters including the barrier height, six diagonal centrifugal distortion constants, and two centrifugal distortion constants (epsilon and epsilon(J)) that characterize the (Delta k = +/-3) matrix elements. The difficulties are discussed that arise in defining a unique model for the torsional terms in the Hamiltonian when a high barrier symmetric top is investigated by distortion moment spectroscopy. The redundancies are investigated that exist in the quartic and sextic Hamiltonian for a near-spherical top such as CH3CF3. (C) 1998 Academic Press.},
keywords = {CH3SIH3, CROSSING MOLECULAR-BEAM, INTERNAL-ROTATION, METHYL SILANE, MICROWAVE FOURIER-TRANSFORM, MILLIMETER-WAVE, POLYATOMIC-MOLECULES, SPECTROSCOPY, SPECTRUM, SYMMETRIC, TOPS},
isbn = {0022-2852},
url = {://000075153100016},
author = {Ozier, I. and Schroderus, J. and Wang, S. X. and McRae, G. A. and Gerry, M. C. L. and Vogelsanger, B. and Bauder, A.}
}
@article {2996,
title = {SUB-DOPPLER SPECTROSCOPY OF THIOFORMALDEHYDE - EXCITED-STATE PERTURBATIONS AND EVIDENCE FOR ROTATION-INDUCED VIBRATIONAL MIXING IN THE GROUND-STATE},
journal = {Journal of Chemical Physics},
volume = {101},
number = {9},
year = {1994},
note = {ISI Document Delivery No.: PP519Times Cited: 9Cited Reference Count: 50},
month = {Nov},
pages = {7300-7310},
type = {Article},
abstract = {High-resolution intracavity dye laser spectroscopy has been used to obtain sub-Doppler spectra of transitions to 350 rotational levels in the 4(0)(1) band of the ($) over tilde A (1)A(2)-($) over tilde X (1)A(1) electronic transition of thioformaldehyde. Ground state combination differences from the sub-Doppler spectra, combined with microwave and infrared data, have been used to improve the ground state rotational and centrifugal distortion constants of H2CS. The upper state shows a remarkable number of perturbations. The largest of these are caused by nearby triplet levels, with matrix elements of 0.05-0.15 cm(-1). A particularly clear singlet-triplet avoided crossing in K-a{\textquoteright} = 7 has been shown to be caused by interaction with the F-1 component of the 3(1)6(2) vibrational level of the ($) over tilde a (3)A(2) state. At least 53\% of the S-1 levels show evidence of very small perturbations by high rovibronic levels of the ground state. The number of such perturbations is small at low J, but increases rapidly beyond J=5 such that 40\%-80\% of the observed S-1 levels of any given J are perturbed by ground state levels. Model calculations show that the density and J dependence of the number of perturbed levels can be explained if there is extensive rotation-induced mixing of the vibrational levels in the ground state.},
keywords = {ANTICROSSING SPECTROSCOPY, HIGH ROVIBRONIC LEVELS, HIGH-RESOLUTION, LASER, LEVEL, OPTICAL DOUBLE-RESONANCE, POLYATOMIC-MOLECULES, POTENTIAL-ENERGY, PYROLYSIS JET SPECTROSCOPY, QUANTUM BEAT SPECTROSCOPY, SINGLET-TRIPLET PERTURBATIONS, SPECTROSCOPY, SURFACES},
isbn = {0021-9606},
url = {://A1994PP51900012},
author = {Clouthier, D. J. and Huang, G. and Adam, A. G. and Merer, A. J.}
}