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|Title: ||THE ANHARMONIC-FORCE FIELD OF ETHYLENE, C2H4, BY MEANS OF ACCURATE AB-INITIO CALCULATIONS|
|Authors: ||MARTIN, Jan|
|Issue Date: ||1995|
|Publisher: ||AMER INST PHYSICS|
|Citation: ||JOURNAL OF CHEMICAL PHYSICS, 103(7). p. 2589-2602|
|Abstract: ||The quartic force field of ethylene, C2H4, has been calculated ab initio using augmented coupled cluster, CCSD(T), methods and correlation consistent basis sets of spdf quality. For the C-12 isotopomers C2H4, C2H3D, H2CCD2, cis-C2H2D2, trans-C2H2D2, C2HD3, and C2D4, all fundamentals are reproduced to better than 10 cm(-1), except for three cases where the error is 11 cm(-1). Our calculated harmonic frequencies suggest a thorough revision of the accepted cm experimentally derived values. Our computed and empirically corrected r(e) geometry differs substantially from experimentally derived values: Both the predicted r(z) geometry and the ground-state rotational constants are, however, in excellent agreement with experiment, suggesting revision of the older values. Anharmonicity constants agree well with experiment for stretches, but differ substantially for stretch-bend interaction constants, due to equality constraints in the experimental analysis that do not hold. Improved criteria for detecting Fermi and Coriolis resonances are proposed and found to work well, contrary to the established method based on harmonic frequency differences that fails to detect several important resonances for C2H4 and its isotopomers. Surprisingly good results are obtained with a small spd basis at the CCSD(T) level. The well-documented strong basis set effect on the v(8) out-of-plane motion is present to a much lesser extent when correlation-optimized polarization functions are used. Complete sets of anharmonic, rovibrational coupling, and centrifugal distortion constants for the isotopomers are available as supplementary material to the paper via the World-Wide Web.|
|Notes: ||UNIV INSTELLING ANTWERP,INST MAT SCI,DEPT CHEM,B-2610 WILRIJK,BELGIUM. NASA,AMES RES CTR,MOFFETT FIELD,CA 94035. SAN DIEGO SUPERCOMP CTR,SAN DIEGO,CA 92186.MARTIN, JML, LIMBURGS UNIV CENTRUM,DEPT SBG,UNIV CAMPUS,B-3590 DIEPENBEEK,BELGIUM.|
|ISI #: ||A1995RP45500022|
|Type: ||Journal Contribution|
|Appears in Collections: ||Research publications|
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