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 1,6-dicarba-closo-hexaborane(6)

The normal mode frequencies and corresponding vibrational assignments of 1,6-dicarba-closo-hexaborane(6) 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-B stretch, B-C stretch, B-H stretch, C-H stretch, B-H bend, and C-H bend) utilizing the D(4h) 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 1,6-dicarba-closo-hexaborane(6) were also calculated and compared against experimental data. A complex pattern of frequency shifts and splittings is revealed.     

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.     

Localized molecular orbital studies on B_4C1_4,1,5-C_2B_3H_5 and B_nH_n~(2-)(n = 6-10, 12)

The wave functions, level energies and Mulliken population analysis of localized molecular orbitals (LMO's) for B4Cl4, 1,5-C2B3H5 and the closo-BnHn2- (n = 6-10, 12) are calculated by using the Edmiston-Reudenberg energy localization scheme under the CNDO/2 approximation in order to reveal the nature of quasi-aromaticity of the closo-BnHn2- (n > 5). It has been found that all the B-H or B-Cl LMO's are highly localized between the B and H (or Cl) atoms, corresponding to B-H or B-Cl o-bond, while the Bn framework bonding is formed mainly by the three-centered two-electron B-B-B bonds on the polyhedral faces. In the cases of B4Cl4 and 1,5-C2B3H5, these three-centered B-B-B bonds just fill their polyhedral faces; however, for the framework bonding of the closo-BnHn2- (n > 5), the valence electron deficiency leads to the delocalization of their three-centered B-B-B bonds, and as delocalizability of this three-centered B-B-B bond increases, some three-centered B-B-B bonds are further delocalized to become a f     

A theoretical study of P4O10: vibrational analysis, infrared and Raman spectra

The normal mode frequencies and the corresponding vibrational assignments of tetraphosphorus decaoxide (P4O10) in tetrahedral (Td) symmetry are examined theoretically and experimentally. The Gaussian 98 set of quantum chemistry codes at the HF/6-311G*, MP2/6-311G*, and DFT/B3LYP/6-311G* levels of theory are used. By comparison to experimental normal mode frequencies deduced by Gilliam et al. [J. Phys. Chem. B 107 (2003) 2892], Chapman [Spectrochim. Acta A, 24 (1968) 1687], Beattie et al. [J. Chem. Soc. A (1970) 449], Konings et al. [J. Mol. Spectrosc. 152 (1992) 29] and the present work, correction factors for predominant vibrational motions are determined and compared. Normal modes were decomposed into five non-redundant motions (P-O stretch, P=O stretch, P-O-P bend, P-O-P wag, and P=O wag). Standard deviations found for the HF, MP2, and DFT corrected frequencies compared to experiment are 9, 5, and 4 cm(-1), respectively. Electron distribution for selected molecular orbitals is considered.     

尿嘧啶和5-氯尿嘧啶1S0→1S2跃迁动态结构的共振拉曼光谱

采用含时量子波包理论的简单模型对5-氯尿嘧啶和尿嘧啶的共振拉曼光谱开展了强度分析拟合, 获得了1(π, π*)激发态的几何结构变化动态特征. 结果表明, 尿嘧啶1S0→1S2跃迁的动态结构特征因5-位氯原子取代而改变. 5-氯尿嘧啶的动态结构特征主要沿C5=C6伸缩振动+C6H12 弯曲振动和N3H9/N1H7弯曲振动+N1C6伸缩振动反应坐标展开, 而尿嘧啶的动态结构特征主要沿嘧啶环的伸缩振动+C5H11/C6H12/N1H7弯曲振动和C4=O10伸缩振动反应坐标展开. π和π*轨道中氯原子的pz电子参与嘧啶环的p-π共轭作用导致了在1(π, π*)激发态上5-氯尿嘧啶的振动重组能更多地配分给嘧啶环的弯曲振动模式和C5=C6伸缩振动模式. 尿嘧啶在甲醇中的激发态动态结构特征与在水中的基本一致, 但波包沿C5H11/C6H12/N1H7弯曲振动+N1C6伸缩振动(υ12)和环呼吸振动(υ17)反应坐标的运动明显增强.     

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.     

Reaction dynamics and vibrational spectroscopy of CH3D molecules with both C-H and C-D stretches excited

State-resolved reactions of CH3D molecules containing both C-H and C-D stretching excitation with Cl atoms provide new vibrational spectroscopy and probe the consumption and disposal of vibrational energy in the reactions. The vibrational action spectra have three different components, the combination of the C-H symmetric stretch and the C-D stretch (nu1 + nu2), the combination of the C-D stretch and the C-H antisymmetric stretch (nu2 + nu4), and the combination of the C-D stretch and the first overtone of the CH3 bend (nu2 + 2nu5). The simulation for the previously unanalyzed (nu2 + nu4) state yields a band center of nu0 = 5215.3 cm(-1), rotational constants of A = 5.223 cm(-1) and B = 3.803 cm(-1), and a Coriolis coupling constant of zeta = 0.084. The reaction dynamics largely follow a spectator picture in which the surviving bond retains its initial vibrational excitation. In at least 80% of the reactive encounters of vibrationally excited CH3D with Cl, cleavage of the C-H bond produces CH2D radicals with an excited C-D stretch, and cleavage of the C-D bond produces CH3 radicals with an excited C-H stretch. Deviations from the spectator picture seem to reflect mixing in the initially prepared eigenstates and, possibly, collisional coupling during the reaction.     

FT-IR and FT-Raman spectra and vibrational investigation of 4-chloro-2-fluoro toluene using ab initio HF and DFT (B3LYP/B3PW91) calculations

FT-IR (4000-100 cm(-1)) and FT-Raman (4000-100 cm(-1)) spectra of solid sample of 4-chloro-2-fluoro toluene (4Cl2FT) have been recorded using Bruker IFS 66 V spectrometer. Ab initio-HF (HF/6-311++G (d, p)) and DFT (B3LYP/6-311++G and B3PW91/6-311++G (d, p)) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, depolarization ratios, IR intensities, Raman activities. The vibrational frequencies are calculated and scaled values are compared with FT-IR and FT-Raman experimental values. The isotropic HF and DFT analyses showed good agreement with experimental observations. The differences between the observed and scaled wave number values of most of the fundamentals are very small in B3LYP than HF. Comparison of the simulated spectra provides important information about the ability of the computational method (B3LYP) to describe the vibrational modes. The influences of substitutions on the geometry of molecule and its normal modes of vibrations have also been discussed. The changes made by substitutions on the benzene are much responsible for the non-linearity of the molecule. This is an attractive entity for the future studies of non-linear optics.     

A theoretical and experimental study of Sb4O6: vibrational analysis, infrared, and Raman spectra

The first ab initio theoretical study of tetraantimony hexoxide (Sb4O6) is reported. The normal mode frequencies, intensities, and the corresponding vibrational assignments of Sb4O6 in T(d) symmetry were calculated using the GAUSSIAN 98 set of quantum chemistry codes at the Hartree-Fock (HF)/CEP-121G, M?ller-Plesset (MP2)/CEP-121G, and density functional theory (DFT)/B3LYP/CEP-121G levels of theory. By comparison to experimental data deduced by our laboratory and others, correction factors for the calculated vibrational frequencies were determined and compared. Normal modes were decomposed into three non-redundant motions (Sb-O-Sb stretch, Sb-O-Sb bend, and Sb-O-Sb wag). Percent relative errors found for the HF, DFT, and MP2 corrected frequencies when compared to experiment are 5.8, 6.1, and 5.7 cm(-1), respectively. Electron distributions for selected molecular orbitals are also considered.     

Vibrational frequencies and structural determination of trimethylarsine oxide

The normal mode frequencies and corresponding vibrational assignments of trimethylarsine oxide 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 (As-C stretch, As=O stretch, C-H stretch, C-As-C bend, As=O bend, H-C-H bend, CH3 wag, and CH3 twist) utilizing the C3v symmetry of the molecule. Calculations were performed at the Hartree-Fock, DFT(B3LYP), and MP2 levels of theory using the standard 6-311G** basis. Calculated infrared intensities and Raman activities are reported.     

CH2BrCl在265 nm光解产生的氯甲基自由基的振动内能

利用离子速度影像技术研究了CH2BrCl在265nm附近的激光光解.利用2+1共振增强多光子电离分别获得光解产物Br(2P1/2)和Br(2P3/2)的离子速度图像,从而得出Br(2P1/2)和Br(2P3/2)的速度分布,以及光解碎片的总平动能分布.据此,运用角动量守恒碰撞模型获得了解离氯甲基自由基(·CH2Cl)的振动内能分布.研究结果表明:CH2BrCl+hv→Br(2P1/2)+CH2Cl通道产生的氯甲基自由基中被激发的振动模主要是v4、v3+v4、v2+v4和v2+v6;CH2BrCl+hv→Br(2P3/2)+CH2Cl通道产生的氯甲基自由基中被激发的振动模主要是v2+v6、v1+v3、v2+v5、v2+v3+v5和v1+v5;母体分子CH2BrCl在吸收光解光子后除有v5(CBrstretch)振动模被激发外,还有v7(CH2a-stretch)等其它振动模也被激发.     

Formation and characterization of thorium methylidene CH2=ThHX complexes

Laser-ablated thorium atoms react with methyl fluoride to give the CH2=ThHF molecule as the major product observed and trapped in solid argon. Infrared spectroscopy, isotopic substitution, and density functional theoretical frequency calculations confirm the identification of this methylidene complex. The four strongest computed absorptions (Th-H stretch, Th=C stretch, CH2 wag, and Th-F stretch) are the four vibrational modes observed. The CH2=ThHCl and CH2=ThHBr species formed from methyl chloride and methyl bromide exhibit the first three of these modes in the infrared spectra. The computed structures (B3LYP and CCSD) show considerable agostic interaction, similar to that observed for the Group 4 CH2=MHX (M = Ti, Zr, Hf) methylidene complexes, and the agostic angle and C=Th bond length decrease slightly in the CH2=ThHX series (X = F, Cl, Br).     

Vibrational frequencies and structural determinations of tert-butylacetylene

The normal mode frequencies and corresponding vibrational assignments of tert-butylacetylene (TBA) are examined theoretically using the Gaussian 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of the nine types of motion (C---C stretch, CC stretch, C---H stretch, C---C---C bend, CC---C bend, CC---H bend, H---C---H bend, CH₃ rock, and CH₃ twist) utilizing the C_3v symmetry of the molecule. Calculations were performed at the Hartree–Fock, B3LYP, and MP2 levels of theory using the standard 6-311G^** basis. Theoretical results were successfully compared against available experimental data.     

Vibrational frequencies and structural determination of tetraazidogermane

The vibrational frequencies and corresponding normal mode assignments of tetraazidogermane are examined theoretically using the Gaussian98 set of quantum chemistry codes. All normal modes were successfully assigned to one of seven types of motion predicted by a group theoretical analysis (N-N-N asymmetric stretch, N-N-N symmetric stretch, Ge-N stretch, N-N-N bend, Ge-N-N bend, N-Ge-N bend, and N-Ge-N-N torsion) utilizing the S(4) symmetry of the molecule. The molecular orbitals of Ge(N(3))(4) are examined.     

Reaction of Cl with CD4 excited to the second C-D stretching overtone

The effects of vibrational excitation on the Cl+CD(4) reaction are investigated by preparing three nearly isoenergetic vibrational states: mid R:3000 at 6279.66 cm(-1), |2100> at 6534.20 cm(-1), and |1110> at 6764.24 cm(-1), where |D(1)D(2)D(3)D(4)> identifies the number of vibrational quanta in each C-D oscillator. Vibrational excitation of the perdeuteromethane is via direct infrared pumping. The reaction is initiated by photolysis of molecular chlorine at 355 nm. The nascent methyl radical product distribution is measured by 2+1 resonance-enhanced multiphoton ionization at 330 nm. The resulting CD(3) state distributions reveal a preference to remove all energy available in the most excited C-D oscillator. Although the energetics are nearly identical, the authors observe strong mode specificity in which the CD(3) state distributions markedly differ between the three Cl-atom reactions. Reaction with CD(4) prepared in the |3000> mode leads to CD(3) products populated primarily in the ground state, reaction with CD(4) prepared in the |2100> mode leads primarily to CD(3) with one quantum of stretch excitation, and reaction with CD(4) prepared in the |1110> mode leads primarily to CD(3) with one quantum of C-D stretch excitation in two oscillators. There are some minor deviations from this behavior, most notably that the Cl atom is able to abstract more energy than is available in a single C-D oscillator, as in the case of |2100>, wherein a small population of ground-state CD(3) is observed. These exceptions likely result from the mixings between different second overtone stretch combination bands. They also measure isotropic and anisotropic time-of-flight profiles of CD(3) (nu(1)=1,2) products from the Cl+CD(4) |2100> reaction, providing speed distributions, spatial anisotropies, and differential cross sections that indicate that energy introduced as vibrational energy into the system essentially remains as such throughout the course of the reaction.     

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 spectroscopic (FT-IR and FT-Raman), first-order hyperpolarizablity, HOMO, LUMO, NBO, Mulliken charges and structure determination of 2-bromo-4-chlorotoluene

The FT-IR and FT-Raman spectra of 2-bromo-4-chlorotoluene (2B4CT) molecule have been recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1), respectively. Optimized geometrical structures, harmonic vibrational frequencies, intensities, reduced mass, force constants and depolarization ratio have been computed by the B3 based (B3LYP) density functional methods using 6-31+G(d,p) and 6-311++G(d,p) basis sets. The observed FT-IR and FT-Raman vibrational frequencies are analysed and compared with theoretically predicted vibrational frequencies. The geometries and normal modes of vibration obtained from DFT method are in good agreement with the experimental data. The Mulliken charges, the natural bonding orbital (NBO) analysis, the values of electric dipole moment (μ) and the first-order hyperpolarizability (β) of the investigated molecule were computed using DFT calculations. The calculated HOMO and LUMO energies show that charge transfer occurs within molecule. The influences of bromine atom, chlorine atom and methyl group on the geometry of benzene and its normal modes of vibrations have also been discussed.     

Vibrations in the B4 rhombic structure

A double minimum six-dimensional potential energy surface (PES) is determined in symmetry coordinates for the most stable rhombic (D2h) B4 isomer in its 1Ag electronic ground state by fitting to energies calculated ab initio. The PES exhibits a barrier to the D4h square structure of 255 cm(-1). The vibrational levels (J=0) are calculated variationally using an approach which involves the Watson kinetic energy operator expressed in normal coordinates. The pattern of about 65 vibrational levels up to 1600 cm(-1) for all stable isotopomers is analyzed. Analogous to the inversion in ammonia-like molecules, the rhombus rearrangements lead to splittings of the vibrational levels. In B4 it is the B1g (D4h) mode which distorts the square molecule to its planar rhombic form. The anharmonic fundamental vibrational transitions of 11B4 are calculated to be (splittings in parentheses): G(0)=2352(22) cm(-1), nu1(A1g)=1136(24) cm(-1), nu2(B1g)=209(144) cm(-1), nu3(B2g)=1198(19) cm(-1), nu4(B2u)=271(24) cm(-1), and nu5(Eu)=1030(166) cm(-1) (D4h notation). Their variations in all stable isotopomers were investigated. Due to the presence of strong anharmonic resonances between the B1g in-plane distortion and the B2u out-of-plane bending modes, the higher overtones and combination levels are difficult to assign unequivocally.     

FT-IR, FT-Raman vibrational spectra and molecular structure investigation of 2-chloro-4-methylaniline: A combined experimental and theoretical study

In this work, the experimental and theoretical vibrational spectra of 2-chloro-4-methylaniline (2Cl4MA, C₇H₈NCl) were studied. FT-IR and FT-Raman spectra of 2Cl4MA in the liquid phase have been recorded in the region 4000–400 cm⁻¹ and 3500–50 cm⁻¹, respectively. The structural and spectroscopic data of the molecule in the ground state have been calculated by using Hartree-Fock (HF) and density functional method (B3LYP) with the 6-31G(d), 6-31G(d,p), 6-31+G(d,p), 6-31++G(d,p) and 6-311G(d), 6-311G(d,p), 6-311+G(d,p), 6-311++G(d,p) basis sets. The vibrational frequencies have been calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The DFT-B3LYP/6-311++G(d,p) calculations have been found more reliable than the ab initio HF/6-311++G(d,p) calculations for the vibrational study of 2Cl4MA. The optimized geometric parameters (bond lengths and bond angles) were compared with experimental values of aniline and p-methylaniline molecules.