Anharmonic force fields of cis- and trans-S1 C2H2

We calculate second-order vibrational perturbation theory (VPT2) anharmonic force fields for the cis and trans conformers of S1 C2H2, and compare the results to experiment. The vibrational assignments of recently observed levels belonging to the cis well are of particular interest. A refined estimate of the cis origin position (44,870 ± 10 cm−1) is proposed, and preliminary low-energy fits to the global J = K = 0 trans level structure are also described. The performance of perturbation theory in this isomerizing system is examined, and both surprising successes and failures are encountered. We examine these and their causes, and offer practical suggestions for avoiding the pitfalls of applying perturbation theory to systems with large amplitude motions.

[1]  A. J. Merer,et al.  Cis-trans isomerization in the S1 state of acetylene: identification of cis-well vibrational levels. , 2011, The Journal of chemical physics.

[2]  A. J. Merer,et al.  EXTENDED PERMUTATION-INVERSION GROUPS FOR SIMULTANEOUS TREATMENT OF THE ROVIBRONIC STATES OF TRANS-ACETYLENE, CIS-ACETYLENE, AND VINYLIDENE , 2011 .

[3]  J. Stanton,et al.  Reduced dimension discrete variable representation study of cis-trans isomerization in the S1 state of C2H2. , 2011, The Journal of chemical physics.

[4]  A. J. Merer,et al.  Direct observation of the symmetric stretching modes of à 1 A u acetylene by pulsed supersonic jet laser induced fluorescence , 2008 .

[5]  A. J. Merer,et al.  Darling-Dennison resonance and Coriolis coupling in the bending overtones of the A 1A(u) state of acetylene, C2H2. , 2008, The Journal of chemical physics.

[6]  A. J. Merer,et al.  New vibrational assignments in the Ā1 Au-[Xtilde] 1Σ+ g electronic transition of acetylene, C2H2: the v′1 frequency , 2003 .

[7]  Rodney J. Bartlett,et al.  Coupled-cluster theory for excited electronic states: The full equation-of-motion coupled-cluster single, double, and triple excitation method , 2001 .

[8]  K. Yamanouchi,et al.  IR−UV Double Resonance Spectroscopy of Acetylene in the Ã1Au nν3‘+ν4‘ and nν3‘+ν6‘ (n = 2, 3) Ungerade Vibrational States† , 2000 .

[9]  P. Taylor,et al.  Benchmark ab initio thermochemistry of the isomers of diimide, N2H2, using accurate computed structures and anharmonic force fields , 1998, physics/9808014.

[10]  A. L. Utz,et al.  Normal modes analysis of Ã‐state acetylene based on directly observed fundamental vibrations , 1993 .

[11]  A. L. Utz,et al.  The direct observation, assignment, and partial deperturbation of ν5 and ν3+ν5 in à 1Au acetylene (C2H2) , 1993 .

[12]  A. L. Utz,et al.  The direct observation, assignment, and partial deperturbation of the ν4 and ν6 vibrational fundamentals in à 1Au acetylene (C2H2) , 1993 .

[13]  M. Herman,et al.  The à electronic state of acetylene: Geometry and axis-switching effects , 1990 .

[14]  Peter R. Taylor,et al.  General contraction of Gaussian basis sets. I. Atomic natural orbitals for first‐ and second‐row atoms , 1987 .

[15]  M. Herman,et al.  The Ã-X̃ band system of acetylene: Bands of the short-wavelength region , 1986 .

[16]  M. Herman,et al.  The Ã-X̃ band system of acetylene: Analysis of medium-wavelength bands, and vibration-rotation constants for the levels nν′3 (n = 4–6), ν′2 + nν′3 (n = 3–5), and ν′1 + nν′3 (n = 2, 3) , 1985 .

[17]  I. Mills.  Vibration-rotation structure in asymmetric and symmetric top molecules , 1972 .

[18]  J. Stanton,et al.  Reduced Dimension DVR Study of cis-trans Isomerization in the S 1 State of C 2 H 2 , 2013 .

[19]  Peter James Stuckey,et al.  With contributions from , 1992 .

[20]  J. Stanton,et al.  Stationary points on the S1 potential energy surface of C2H2 , 1994 .

[21]  K. Rao,et al.  Molecular Spectroscopy: Modern Research , 1972 .