@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 {690,
title = {New vibrational assignments in the (A)over-tilde(1) A(u)-(X)over-tilde (1)Sigma(+)(g) electronic transition of acetylene, C2H2: the nu({\textquoteright})(1) frequency},
journal = {Molecular Physics},
volume = {101},
number = {4-5},
year = {2003},
note = {ISI Document Delivery No.: 657RRTimes Cited: 9Cited Reference Count: 27},
pages = {663-673},
type = {Article},
abstract = {New laser-induced fluorescence spectra of supersonic jet cooled acetylene (C2H2) in the wavelength region 230-205 nm have led to an improved understanding of the vibrational structure of the (A) over tilde (1)A(u) state. Among the new bands observed are two weak perturbed bands at 46008 cm(-1) and 46116 cm(-1). Rotational analyses of these bands, together with the corresponding {\textquoteright}hot{\textquoteright} bands arising from the ground state v(4) fundamental, have shown that the upper states have asymmetric top K structure that is unaffected by a axis Coriolis coupling; this means that they do not involve overtones of the low frequency bending vibrations and therefore must be combinations of a(g) vibrational normal modes. From their positions in the manifold, their vibrational assignments can only be 2(0)(2)3(0)(1) and 1(0)(1)3(0)(1). These assignments lead to values of x(22){\textquoteright}, x(13){\textquoteright}, and a revised value for the symmetric CH stretching frequency, v(1){\textquoteright} = 2880.5 cm(-1); this revised value is 160 cm(-1) lower than the previously accepted value, but consistent with new ab initio calculations that we performed at the EOM-CCSD level using a TZ2P ( triple-zeta plus double polarization) basis set.},
keywords = {BANDS, MODES, PARTIAL DEPERTURBATION, ROTATION CONSTANTS, SPECTROSCOPY, SPECTRUM, STATE, WAVELENGTH, X BAND SYSTEM},
isbn = {0026-8976},
url = {://000181680600017},
author = {Merer, A. J. and Yamakita, N. and Tsuchiya, S. and Stanton, J. F. and Duan, Z. C. and Field, R. W.}
}