Coupled-cluster study of the rotational and inversion barrier heights, equilibrium geometries and vibrational frequencies of methylamine

2005 ◽  
Vol 414 (4-6) ◽  
pp. 495-499 ◽  
Author(s):  
Marina Pelegrini ◽  
Orlando Roberto-Neto ◽  
Francisco B.C. Machado
Keyword(s):  
Vibrational Frequencies ◽  
Coupled Cluster ◽  
Inversion Barrier ◽  
Barrier Heights ◽  
And Inversion ◽  
Equilibrium Geometries

Vibrational analysis of the low resolution absorption spectra of BrClCS and Br2CS

1988 ◽  
Vol 66 (3) ◽  
pp. 359-366 ◽  
Author(s):  
B. Simard ◽  
R. P. Steer ◽  
R. H. Judge ◽  
D. C. Moule
Keyword(s):  
Absorption Spectra ◽  
Room Temperature ◽  
Vibrational Analysis ◽  
Vibrational Frequencies ◽  
Low Resolution ◽  
Barrier Heights ◽  
Vibrational Levels ◽  
Out Of Plane ◽  
The Given

The [Formula: see text] absorption spectra of BrClCS and Br2CS have been photographed under low resolution at room temperature. The electronic origins of BrClCS and Br2CS have been placed at 17116 and 16859 cm−1, respectively. Vibronic analyses show that the molecules are non-planar in their ā states. By fitting quadratic–Gaussian and quadratic–quartic double-minimum potentials to the observed vibrational levels of the out-of-plane manifolds, the equilibrium out-of-plane angles and the barrier heights to molecular inversion have been estimated to be 25 ± 1 deg and 541 ± 10 cm−1 for BrClCS, and 17.5 ± 1 deg and 524 ± 10 cm−1 for Br2CS. In the case of BrClCS, all six ā state vibrational frequencies have been obtained. In the case of Br2CS, only modes 1 (C—S stretch), 2 (symmetric C—Br stretch), 3 (in-plane Br—C—Br scissor), and 4 (out-of-plane bend) are active in the spectrum. Comparisons with other tetraatomic thiocarbonyls support the given assignments.

The Fock-Space Coupled-Cluster Method in the Calculation of Excited State Properties

2005 ◽  
Vol 70 (6) ◽  
pp. 811-825 ◽  
Author(s):  
Monika Musiał ◽  
Leszek Meissner
Keyword(s):  
Experimental Data ◽  
Excited States ◽  
Fock Space ◽  
Hamiltonian Formulation ◽  
Basis Sets ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Excitation Energies ◽  
Equilibrium Geometries

Our recently developed intermediate Hamiltonian Fock-space coupled-cluster (FS-CC) method with singles and doubles is applied to calculation of equilibrium geometries, harmonic frequencies and adiabatic excitation energies for some excited states of N2 and CO. Due to the intermediate Hamiltonian formulation, which provides a robust computational scheme for solving the FS-CC equations, and the efficient factorization strategy, relatively large basis sets and reference spaces are employed permitting a comparison of calculated properties with experimental data.

Approximating Coupled Cluster Level Vibrational Frequencies with Composite Methods

2006 ◽  
Vol 110 (8) ◽  
pp. 2796-2800 ◽  
Author(s):  
Yanping Fan ◽  
Junming Ho ◽  
Ryan P. A. Bettens
Keyword(s):  
Vibrational Frequencies ◽  
Coupled Cluster ◽  
Composite Methods ◽  
Cluster Level
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