Vibrational frequencies and structural determination of trichloroboroxine

The normal mode frequencies and corresponding vibrational assignments of trichloroboroxine (B3O3Cl3) in D3h symmetry are examined theoretically using the Gaussian 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of five types of motion (B-Cl stretch, B-O stretch, B-Cl bend, O-B-O bend, and B(OOCl) umbrella motion) predicted by a group theoretical analysis. By comparing the vibrational frequencies with IR and Raman spectra available in the literature, a set of scaling factors is derived. Molecular orbitals and bonding are examined.     

Vibrational frequencies and structural determination of adamantane

The normal mode frequencies and corresponding vibrational assignments of adamantane in Td symmetry are examined theoretically using the Gaussian 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of eight types of motion predicted by a group theoretical analysis. The vibrational modes of the deuterated form of adamantane were also calculated and compared against experimental data.     

IR spectroscopic investigation of cis-(CH(3))(2)Au(O,O'-acac) and cis-(CD(3))(2)Au(O,O'-acac)

The IR spectrum of cis-(CH(3))(2)Au(O,O'-acac) has been reassigned by comparing frequencies for cis-(CH(3))(2)Au(O,O'-acac) and cis-(CD(3))(2)Au(O,O'-acac), and by analysis of the DFT-calculated normal modes and their frequencies for the isolated molecules. The vibrational intensity in the C-H stretching region arises almost entirely from the cis-(CH(3))(2)Au fragment, while the methyl deformation intensity is largely of acetylacetonato ligand origin. A low frequency mode in the C-H stretching region is the first overtone of the delta(a)(CH(3)) mode of cis-(CH(3))(2)Au. The Au-C stretching modes are affected by deuteration of the cis-(CH(3))(2)Au fragment, while the Au-O stretching modes are not.     

Vibrational frequencies and structural determination of tetraiododiphosphine

The normal mode frequencies and corresponding vibrational assignments of of tetraiododiphosphine in C2h symmetry are examined theoretically using the Gaussian 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of six types of motion (P-I stretch, P-P stretch, PI2 scissors, PI2 twist, PI2 wag, and PI2 rock) predicted by a group theoretical analysis. Computed vibrational frequencies are with IR and Raman spectra available in the literature, and uniform scaling factors are derived. Theoretical IR and Raman intensities are reported.     

Vibrational frequencies and structural determination of digermyl ether

The normal mode frequencies and corresponding vibrational assignments of digermyl ether in C(2v) symmetry are examined theoretically using the Gaussian 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of six types of motion (Ge-H stretch, Ge-O stretch, Ge-O-Ge bend, H-Ge-H bend, GeH(3) wag, and GeH(3) twist) predicted by a group theoretical analysis. By comparing the vibrational frequencies with IR and Raman spectra available in the literature, a set of scaling factors is derived. Predicted infrared and Raman intensities are reported.     

Vibrational frequencies and structural determinations of 1,5-dicarba-closo-pentaborane(5)

The normal mode frequencies and corresponding vibrational assignments of 1,5-dicarba-closo-pentaborane(5) are examined theoretically using the GAUSSIAN 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of six types of motion predicted by a group theoretical analysis (C-H stretch, B-H stretch, B-B stretch, B-C stretch, C-H wag, and B-H wag) utilizing the D(3h) symmetry of the molecule. By comparing the vibrational frequencies with IR and Raman spectra available in the literature, a set of scaling factors is derived. Theoretical IR and Raman intensities are reported.     

Vibrational frequencies and structural determinations of tetrachlorobutatriene

The normal mode frequencies and corresponding vibrational assignments of tetrachlorobutatriene in D2h symmetry are examined theoretically using the Gaussian 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of the six types of motion (C=C stretch, CCl2 scissors, CCl2 twist, CCl2 wag, CCl2 rock, and C=C=C bend) predicted by a group theoretical analysis. By comparing the vibrational frequencies with IR and Raman spectra available in the literature, a set of scaling factors is derived.     

Vibrational frequencies and structural determinations of tetraisocyanatosilane

The normal mode frequencies and corresponding vibrational assignments of Si(NCO)(4) are examined theoretically using the GAUSSIAN 98 set of quantum chemistry codes. Each of the vibrational modes was assigned to one of six types of motion predicted by a group theoretical analysis (Si-N stretch, N-C-O symmetric stretch, N-C-O asymmetric stretch, N-C-O bend, Si-N-C bend, and N-Si-N bend) utilizing the T(d) symmetry of the molecule. Uniform scaling factors were derived for each type of motion. Predicted infrared and Raman intensities are reported.     

Vibrational frequencies and structural determination of aluminum tetrahydroborate

The normal mode frequencies and corresponding vibrational assignments of aluminum tetrahydroborate in D3 symmetry are examined theoretically using the 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of seven types of motion (B-H stretch, Al-B stretch, B-Al-B bend, H-B-H bend, BH4 wag, BH4 rock, and BH4 twist) predicted by a group theoretical analysis. By comparing the vibrational frequencies with infrared and Raman spectra available in the literature, a set of scaling factors is derived. Theoretical infrared intensities and Raman activities are reported.     

Vibrational frequencies and structural determination of Al(8)S(12)

The normal mode frequencies and corresponding vibrational assignments of Al(8)S(12) in T(h) symmetry are examined theoretically using the Gaussian98 set of quantum chemistry codes. All normal modes were successfully assigned to one of four types of motion (Al-S stretch, Al-S-Al bend, S-Al-S bend, and Al-S-Al wag) predicted by a group theoretical analysis. Normal mode frequencies are predicted and calculated infrared intensities and Raman activities are presented. The thermodynamics of the reaction 2Al(4)S(6)-->Al(8)S(12) are examined.     

Vibrational frequencies and structure of B4Cl4: an ab intio quantum chemical study

The normal mode frequencies and corresponding vibrational assignments of B4Cl4 are examined theoretically using the Gaussian 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of three types of motion predicted by a group theoretical analysis (B-B stretch, B-Cl stretch, B-Cl bend) utilizing the Td symmetry of the molecule. The vibrational modes of the naturally isotopically substituted (1-(10)B, 2-(10)B, 3-(10)B and 4-(10)B) forms of B4Cl4 were also calculated and compared against experimental data. A complex pattern of frequency shifts and splittings is revealed.     

Relating normal vibrational modes to local vibrational modes with the help of an adiabatic connection scheme

Information on the electronic structure of a molecule and its chemical bonds is encoded in the molecular normal vibrational modes. However, normal vibrational modes result from a coupling of local vibrational modes, which means that only the latter can provide detailed insight into bonding and other structural features. In this work, it is proven that the adiabatic internal coordinate vibrational modes of Konkoli and Cremer [Int. J. Quantum Chem. 67, 29 (1998)] represent a unique set of local modes that is directly related to the normal vibrational modes. The missing link between these two sets of modes are the compliance constants of Decius, which turn out to be the reciprocals of the local mode force constants of Konkoli and Cremer. Using the compliance constants matrix, the local mode frequencies of any molecule can be converted into its normal mode frequencies with the help of an adiabatic connection scheme that defines the coupling of the local modes in terms of coupling frequencies and reveals how avoided crossings between the local modes lead to changes in the character of the normal modes.     

Vibrational frequencies and structural determinations of 3,5-dibromo-1,2,4-trithia-3,5-diborolane

The vibrational frequencies and corresponding normal mode assignments of 3,5-dibromo-1,2,4-trithia-3,5-diborolane (B2S3Br2) are examined theoretically using the Gaussian98 set of quantum chemistry codes. All normal modes were successfully assigned to one of six types of motion predicted by a group theoretical analysis (B-S stretch, B-Br stretch, S-S stretch, S-B-S bend, B-Br wag, B(SSBr) umbrella motion) utilizing the C2v symmetry of the molecule. The vibrational modes of the naturally isotopically substituted (1-10B and 2-10B) forms of B2S3Br2 were also calculated and compared against experimental data. The molecular orbitals of B2S3Br2 are examined. The calculations suggest that a considerable amount of pi bonding occurs in B2S2Br2.     

Contributions of the 8-methyl group to the vibrational normal modes of flavin mononucleotide and its 5-methyl semiquinone radical

Resonance Raman spectroscopy is a powerful tool to investigate flavins and flavoproteins, and a good understanding of the flavin vibrational normal modes is essential for the interpretation of the Raman spectra. Isotopic labeling is the most effective tool for the assignment of vibrational normal modes, but such studies have been limited to labeling of rings II and III of the flavin isoalloxazine ring. In this paper, we report the resonance and pre-resonance Raman spectra of flavin mononucleotide (FMN) and its N5-methyl neutral radical semiquinone (5-CH 3FMN(*)), of which the 8-methyl group of ring I has been deuterated. The experiments indicate that the Raman bands in the low-frequency region are the most sensitive to 8-methyl deuteration. Density functional theory (DFT) calculations have been performed on lumiflavin to predict the isotope shifts, which are used to assign the calculated normal modes to the Raman bands of FMN. A first assignment of the low-frequency Raman bands on the basis of isotope shifts is proposed. Partial deuteration of the 8-methyl group reveals that the changes in the Raman spectra do not always occur gradually. These observations are reproduced by the DFT calculations, which provide detailed insight into the underlying modifications of the normal modes that are responsible for the changes in the Raman spectra. Two types of isotopic shift patterns are observed: either the frequency of the normal mode but not its composition changes or the composition of the normal mode changes, which then appears at a new frequency. The DFT calculations also reveal that the effect of H/D-exchange in the 8-methyl group on the composition of the vibrational normal modes is affected by the position of the exchanged hydrogen, i.e., whether it is in or out of the isoalloxazine plane.     

Vibrational frequencies and structural determination of Ge4O4

The vibrational frequencies and corresponding normal mode assignments of the germanium monoxide tetramer (Ge4O4) in Td symmetry are examined theoretically using the Gaussian03 set of quantum chemistry codes and compared against available experimental data. All normal modes were successfully assigned to one of two types of motion predicted by a group theoretical analysis (Ge-O stretch and Ge-O-Ge bend) utilizing the Td symmetry of the molecule. The molecule possesses a cubane-like structure.     

Vibrational frequencies and structural determination of phosphorous tricyanide

The normal mode frequencies and corresponding vibrational assignments of phosphorous tricyanide (P(CN)(3)) are examined theoretically using the Gaussian98 set of quantum chemistry codes. Each of the vibrational modes was assigned to one of four types of motion predicted by a group theoretical analysis P-C stretch, CN stretch, P-C[triple bond]C bend, and C-P-C bend) utilizing the C(3v) symmetry of the molecule. A uniform scaling factor was derived for each type of motion. Predicted infrared and Raman intensities are reported.     

Vibrational frequencies and structural determination of dicyanodifluorosulfur

The normal mode frequencies and corresponding vibrational assignments of dicyanodifluorosulfur are examined theoretically using the Gaussian03 set of quantum chemistry codes. Each of the vibrational modes was assigned to one of six types of motion predicted by a group theoretical analysis (CN stretch, SC stretch, SF stretch, FSC bend, SCN bend, and CSC bend) utilizing the C(2v) symmetry of the molecule. A set of uniform scaling factors was derived for each type of motion. Predicted infrared and Raman intensities are reported.     

Exploring the localized-to-delocalized boundary in mixed-valence systems using infrared spectroelectrochemistry

Infrared spectroelectrochemistry has been used to explore the vibrational properties of a pyrazine-bridged osmium-polypyridine dimer as a function of its formally metal-centered oxidation states (i.e., Os(II)Os(II), Os(II)Os(III), and Os(III)Os(III)). The infrared spectrum of the "mixed-valent" species is particularly interesting and exhibits features consistent with both electronic localization and delocalization on the vibrational time scale, as revealed by the presence of both (i) a highly active totally symmetric mode from the bridging pyrazine ligand (nu(8a)), and (ii) total coalescence of at least four modes from peripheral bipyridine ligands. The nature and origin of the observed peaks were confirmed by analysis of the shifts in vibrational frequencies accompanying deuteration of pyrazine and also by comparison of the data for the dimeric complexes with those for the parent monomers.     

Vibrational frequencies and structural determination of hafnium tetrahydroborate

The normal mode frequencies and corresponding vibrational assignments of of hafnium tetrahydroborate in T symmetry are examined theoretically using the Gaussian 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of to one of six types of motion (B-H stretch, Hf-B stretch, B-Hf-B bend, H-B-H bend, BH4 wag, and BH4 twist) predicted by a group theoretical analysis. By comparing the vibrational frequencies with IR and Raman spectra available in the literature, a set of scaling factors is derived. Theoretical IR and Raman intensities are reported. Quantum chemical calculations predict that the molecule does not possess strict Td symmetry. The Td structure possesses one negative eigenvalue. The minimum energy structure possesses T symmetry.     

Vibrational frequencies and structural determination of 1,3-dichloro-1,3-diazetidine-2,4-dione

The normal mode frequencies and corresponding vibrational assignments of 1,3-dichloro-1,3-diazetidine-2,4-dione are examined theoretically using the Gaussian 98 set of quantum chemistry codes. Each of the vibrational modes was assigned to one of six types of motion predicted by a group theoretical analysis (C=O stretch, N-C stretch, N-Cl stretch, N-C-N bend, N-Cl bend, and C=O bend) utilizing the C2h symmetry of the molecule. Uniform scaling factors was derived for each type of motion. Predicted infrared and Raman intensities are reported.