ASYM20: A Program for Force Constant and Normal Coordinate Calculations, with a Critical Review of the Theory Involved

Hedberg, Lise; Mills, Ian

doi:10.1006/jmsp.1993.1162

Cited by 423 publications

(289 citation statements)

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“…[53] Furthermore, we also accepted the bond angles of the dimer and trimer from the computation. We also carried out normal coordinate analyses using the program ASYM [54] based on the computed frequencies and force fields of all three species, in order to calculate vibrational amplitudes. These were used as starting parameters, and many of them were later refined during the analysis.…”

Section: Methodsmentioning

confidence: 99%

The Elusive Structure of CrCl₂—A Combined Computational and Gas‐Phase Electron‐Diffraction Study

Vest

Varga

Hargittai

et al. 2008

Chemistry A European J

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Chromium dichloride poses a challenge to the structural chemist. Its different forms of aggregation and association display all well-known structural distortions induced by vibronic interactions. The monomeric molecule has a Renner-Teller distorted bent geometry, the crystal exhibits strong Jahn-Teller distortion, and the oligomers have slightly distorted four-membered-ring structures due to the pseudo-Jahn-Teller effect. In this paper we report on the low-energy structures of the monomer and its clusters, Cr(2)Cl(4), Cr(3)Cl(6), and Cr(4)Cl(8), from unrestricted Kohn-Sham (broken-symmetry) density functional calculations. CrCl(2) was also investigated at higher level, including coupled-cluster and state-average CASSCF computations. The global minima of the gas-phase clusters consist of two-dimensional, antiferromagnetically coupled chains of CrCl(2) units forming four-membered, doubly bridged Cr(2)Cl(2) rings, closely resembling the solid-state structure of alpha-CrCl(2). Each Cr atom in these chains has spin quantum number S=2. This suggests that the CrCl(2) nucleation starts very early on the structural chain motif found in the solid. There is only a very small change in energy from the antiferromagnetically to the ferromagnetically coupled Cr atoms, which indicates little spin-coupling between the metal centers. There is an approximately constant change in energy, about 50 kcal mol(-1), with every new CrCl(2) unit during cluster formation. Information about the structure of these clusters was used in the re-analysis of high-temperature electron-diffraction data. The vapor at 1170 K contained about 77 % monomeric molecules, 19 % dimers, and a small amount of trimers. Monomeric CrCl(2) was found to be bent with a bond angle of 149(10) degrees, in good agreement with our computations, which resulted in a Renner-Teller distortion of the lowest-energy (5)Pi(g) electronic state into the bent (5)B(2) ground state. The vibrational spectrum of chromium dichloride is discussed and the thermodynamics of cluster formation from 1000-2000 K is examined.

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Section: Methodsmentioning

confidence: 99%

The Elusive Structure of CrCl₂—A Combined Computational and Gas‐Phase Electron‐Diffraction Study

Vest

Varga

Hargittai

et al. 2008

Chemistry A European J

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“…optimization of a number of scale factors, the complete force Ðeld is Ðtted to experimental fundamentals by a least-squares method using the ASYM40 program. 54 This program was also used to calculate the B-matrix and to obtain the PED (potential energy distribution) in the normal coordinate system. The scale factors deÐned for each type of coordinate and for each ab initio Ðeld are shown in Table 5.…”

Section: Vibrational Calculationsmentioning

confidence: 99%

“…54 We used the theoretical geometry (Table 1) without any empirical correction. Figure 1 shows the internal coordinate deÐnitions.…”

Section: Vibrational Calculationsmentioning

confidence: 99%

Vibrational spectrum of pyridazine

Vázquez

Gozález

Márquez

et al. 1998

J. Raman Spectrosc.

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“…The scale factors (see Table 4) were obtained from NMe(SiH 3 ) 2 [9] and SiH 3 SiHCl 2 [10]. The HF/6-31G(d) cartesian force field and atomic cartesian coordinates output were input into the program ASYM40 (an up-date of ASYM20 [17]) for transformation into an internal coordinate system, with output of valence force constants and frequencies for partially deuteriated isotopomers. The potential energy associated with the stretching of the two Si±H or Si±Cl bonds in each molecule is given by…”

Section: Methodsmentioning

confidence: 99%

Bis(dichlorosilyl)methylamine - Synthesis, Crystal Structure, and Conformational Analysis in the Gas Phase

Fleischer

McKean

Parsons

et al. 1999

Z. anorg. allg. Chem.

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A straightforward preparation has been found for bis(dichlorosilyl)methylamine, (SiHCl2)2NMe (1), involving reaction between H2NMe and an excess of SiHCl3, dissolved either in pentane or THF at 253 K. 1 and a side‐product, 1,3,5‐trichloro‐2,4,6‐trimethylcyclotrisilazane, (–SiHCl–NMe–)3 (2), were identified by elemental analysis, mass spectrometry and 1H‐NMR‐spectroscopy. Some physical, NMR‐ and IR spectroscopical properties of 1 were determined. The molecular and crystal structure of 1 was investigated by single crystal X‐ray diffraction. Selected structural parameters: r(Si–N) 169.7(5), r(Si–Cl) 203.1(2)–204.4(2), r(C–N) 150.0(8) pm; a(SiNSi) 123.6(3), a(SiNC) 118.3(4)/118.0(4)°. Ab initio force field data and infrared intensities were calculated for four conformers of 1. Comparison of the observed and calculated IR spectra favours the two structures found ab initio provided that their actual abundancies are different from those calculated.

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ASYM20: A Program for Force Constant and Normal Coordinate Calculations, with a Critical Review of the Theory Involved

Cited by 423 publications

References 0 publications

The Elusive Structure of CrCl₂—A Combined Computational and Gas‐Phase Electron‐Diffraction Study

The Elusive Structure of CrCl₂—A Combined Computational and Gas‐Phase Electron‐Diffraction Study

Vibrational spectrum of pyridazine

Bis(dichlorosilyl)methylamine - Synthesis, Crystal Structure, and Conformational Analysis in the Gas Phase

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ASYM20: A Program for Force Constant and Normal Coordinate Calculations, with a Critical Review of the Theory Involved

Cited by 423 publications

References 0 publications

The Elusive Structure of CrCl2—A Combined Computational and Gas‐Phase Electron‐Diffraction Study

The Elusive Structure of CrCl2—A Combined Computational and Gas‐Phase Electron‐Diffraction Study

Vibrational spectrum of pyridazine

Bis(dichlorosilyl)methylamine - Synthesis, Crystal Structure, and Conformational Analysis in the Gas Phase

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Product

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The Elusive Structure of CrCl₂—A Combined Computational and Gas‐Phase Electron‐Diffraction Study

The Elusive Structure of CrCl₂—A Combined Computational and Gas‐Phase Electron‐Diffraction Study