The vibrational spectra (100–1600 cm−1) and scaled 3-21G abinitio harmonic force fields for 7-oxanorbornane and 7-thianorbornane

1989 ◽  
Vol 67 (3) ◽  
pp. 535-544 ◽  
Author(s):  
R. A. Shaw ◽  
N. Ibrahim ◽  
H. Wieser
Keyword(s):  
Force Field ◽  
Dimethyl Ether ◽  
Vibrational Spectra ◽  
Force Fields ◽  
Harmonic Force ◽  
Scaling Factors

The vibrational spectra in the region of 1600–100 cm−1 are reported for 7-oxa- and 7-thianorbornane. Abinitio 3-21G harmonic force fields based on optimized structures determined previously at the same level of theory were calculated for both molecules. The vibrational spectra were assigned unambiguously and almost completely with the aid of the 3-21G force fields, scaled using ten factors previously optimized in an overlay refinement to fit assigned frequencies of norbornane, norbornene, and norbomadiene, and including two others, where appropriate, from dimethyl ether and thietane. Reoptimization of 12 scaling factors reproduced 60 assigned frequencies out of a total of 70 in the specified region with average errors of 7.4 and 4.9 cm−1, respectively, for the two molecules. The final refinement changed the scaling factors transferred from norbornane generally by less than 1%. Keywords: 7-oxanorborane, 7-thianorborane, vibrational spectra, abinitio harmonic force field.

Comparison of STO-3G and 3-21G ab initio harmonic force fields for ethane, propane, dimethyl ether, and cyclobutane: effects of geometry and scaling on calculated frequencies, eigenvectors, and infrared absorption intensities

1988 ◽  
Vol 66 (5) ◽  
pp. 1318-1332 ◽  
Author(s):  
R. Anthony Shaw ◽  
Charles Ursenbach ◽  
Arvi Rauk ◽  
Hal Wieser
Keyword(s):  
Force Field ◽  
Ab Initio ◽  
Dimethyl Ether ◽  
Infrared Absorption ◽  
Force Fields ◽  
Vibrational Frequencies ◽  
Harmonic Force ◽  
Scaling Factors ◽  
Bond Lengths ◽  
Optimized Geometries

Ab initio harmonic force fields were calculated for ethane, propane, dimethyl ether, and cyclobutane at the STO-3G and 3-21G levels. The calculated frequencies, displacement eigenvectors, and calculated infrared absorption intensities were compared as they derive from force constants that were (i) unsealed; (ii) scaled to fit observed vibrational frequencies reported in the literature; (iii) evaluated at the optimized geometries; and (iv) evaluated at structures for which the bond lengths were corrected from the optimized geometries according to published procedures. A total of nine combinations of ab initio force field/reference geometry/G-matrix geometry were investigated for each of the four molecules. The ability of scaling factors as the only variables to predict vibrational parameters from STO-3G and 3-21G force fields was explored. Conditions were examined for which the scaling factors are satisfactorily transferable among different molecules.

Vibrational spectra of stannane: Harmonic force field, Raman and IR intensities from ab initio correlated wavefunctions

1989 ◽  
Vol 130 (1-3) ◽  
pp. 451-456 ◽  
Author(s):  
Javier Fernandez Sanz ◽  
Antonio Marquez ◽  
Claude Pouchan
Keyword(s):  
Force Field ◽  
Ab Initio ◽  
Vibrational Spectra ◽  
Harmonic Force ◽  
Ir Intensities

The harmonic force field and vibrational spectra of pyrrole

1986 ◽  
Vol 58 (2) ◽  
pp. 401-411 ◽  
Author(s):  
Yaoming Xie ◽  
Kangnian Fan ◽  
James E. Boggs
Keyword(s):  
Force Field ◽  
Vibrational Spectra ◽  
Harmonic Force

The vibrational spectra (100–1500 cm−1) of a series of bicyclo[3.2.1]octanes assigned by means of scaled 3-21G ab initio harmonic force fields

1993 ◽  
Vol 71 (4) ◽  
pp. 578-609 ◽  
Author(s):  
Thomas Eggimann ◽  
Nan Ibrahim ◽  
R. Anthony Shaw ◽  
Hal Wieser
Keyword(s):  
Ab Initio ◽  
Vibrational Spectra ◽  
Force Fields ◽  
Basis Set ◽  
Average Error ◽  
Field Scale ◽  
Harmonic Force ◽  
First Time ◽  
Derivatives Of ◽  
Phase Spectra

The infrared absorption (vapor phase and solution) and Raman (liquid phase) spectra of bicyclo[3.2.1]octane, 8-oxabicyclo[3.2.1]octane, 6-oxabicyclo[3.2.1]octane, 6,8-dioxabicyclo[3.2.1]octane, and the 7,7-dideutero-substituted derivatives of the last two compounds are reported in the region 100–1500 cm−1 for the first time. The vibrational spectra are assigned almost completely with the guidance of ab initio 3-21G geometries and scaled force fields. A total of 14 force-field scale facors are transferred from smaller molecules, predicting the frequencies with an average error of 7.6 cm−1 (1.2%) for 196 assigned transitions. After optimizing the factors in an overlay refinement involving all six molecules, the frequencies are within 5.7 cm−1 (0.75%) of experiment. The ab initio absorption and Raman intensities are calculated with the 3-21G basis set and are demonstrated to be of such accuracy as to be useful for the spectral assignments. These intensities are calculated with uniformly and nonuniformly scaled force fields and compared to the experimental spectra. The intensities derived from the latter force fields are superior, meaning that nonuniform scaling is preferable at this level of theory for both vibrational frequencies and normal mode descriptions.

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