Resonance Raman study of short-time photodissociation dynamics of the charge-transfer band absorption of nitrobenzene in cyclohexane solution

Resonance Raman spectra were obtained for nitrobenzene in cyclohexane solution with excitation wavelengths in resonance with the charge-transfer (CT) band absorption spectrum. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion mainly along the nominal NO2 symmetric stretch mode (nu 11), the nominal benzene ring stretch mode (nu 7), accompanied by a moderate degree of motion along the nominal ONO symmetry bend/benzene ring stretch mode (nu 23), the nominal C-N stretch/benzene ring breathing mode (nu 16), the nominal CCC bending mode (nu 20) and the nominal CCH in-plane bending mode (nu 14). A preliminary resonance Raman intensity analysis was done and the results for nitrobenzene were compared to previously reported results for several nitroalkanes.     

Resonance Raman investigation of the short-time photodissociation dynamics of the charge-transfer absorption of the I2-benzene complex in benzene solution

Resonance Raman spectra were obtained for the I2-benzene complex in benzene solvent with excitation wavelengths in resonance with the CT-band absorption. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion mainly along the nominal I-I stretch mode nu(18), the nominal symmetric benzene ring stretch mode nu5, and the nominal symmetric CCH bending nu7. There is also a small contribution from the nominal out-of-plane CH oop wag nu15. A preliminary resonance Raman intensity analysis was done, and the results for the I2-benzene complex were compared to results previously reported for the 1-hexene-I2 complex. We briefly discuss the differences and similarities in the CT-band absorption excitation of an I2-benzene complex relative to those of an I2-alkene complex.     

Resonance Raman intensity analysis of the excited state proton transfer dynamics of 2-nitrophenol in the charge-transfer band absorption

Resonance Raman spectra were obtained for 2-nitrophenol in cyclohexane solution with excitation wavelengths in resonance with the charge-transfer (CT) proton transfer band absorption. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion along more than 15 normal modes: the nominal CCH bend+CC stretch nu(12) (1326 cm(-1)), the nominal CCC bend nu(23) (564 cm(-1)), the nominal CO stretch+NO stretch+CC stretch nu(14) (1250 cm(-1)), the nominal CCH bend+CC stretch+COH bend nu(15) (1190 cm(-1)); the nominal CCH bend+CC stretch nu(17) (1134 cm(-1)), the nominal CCC bend+CC stretch nu(22) (669 cm(-1)), the nominal CCN bend nu(27) (290 cm(-1)), the nominal NO(2) bend+CC stretch nu(21) (820 cm(-1)), the nominal CCO bend+CNO bend nu(25) (428 cm(-1)), the nominal CC stretch nu(7) (1590 cm(-1)), the nominal NO stretch nu(8) (1538 cm(-1)), the nominal CCC bend+NO(2) bend nu(20) (870 cm(-1)), the nominal CC stretch nu(6) (1617 cm(-1)), the nominal COH bend+CC stretch nu(11) (1382 cm(-1)), nominal CCH bend+CC stretch nu(9) (1472 cm(-1)). A preliminary resonance Raman intensity analysis was done and the results for 2-nitrophenol were compared to previously reported results for nitrobenzene, p-nitroaniline, and 2-hydroxyacetophenone. The authors briefly discuss the differences and similarities in the CT-band absorption excitation of 2-nitrophenol relative to those of nitrobenzene, p-nitroaniline, and 2-hydroxyacetophenone.     

Resonance Raman intensity analysis of the excited-state proton-transfer dynamics of 2-hydroxybenzaldehyde in the charge-transfer/proton-transfer absorption band

Resonance Raman spectra were obtained for 2-hydroxybenzaldehyde (OHBA) in cyclohexane solution with excitation wavelengths in resonance with the first charge-transfer/proton-transfer (CT/PT) band absorption. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion predominantly along the nominal C=CH in-plane bend+ring deformation modes (nu9, nu10, nu14, nu16, nu18, nu19, nu20, nu26, nu30, nu31, and nu35) accompanied by a smaller amount of motion along the nominal C=O stretch mode (nu7), the nominal C=C-C(=O) in-plane bend modes (nu33 and nu37), and the nominal ring C-O-H in-plane bend modes (nu9 and nu14). A preliminary resonance Raman intensity analysis was done, and these results for the OHBA molecule were compared to results previously reported for the 2-hydroxyacetophenone (OHAP) molecule. Several proton-transfer tautomers in the ground and excited states were predicted from the results of B3LYP/cc-PVTZ, UB3LYP/cc-PVTZ, and CASSCF/cc-PVDZ level of theory computations. The differences and similarities between the CT/PT band resonance Raman spectra and the vibrational reorganizational energies for the OHBA molecule relative to those for the OHAP molecule are briefly discussed.     

Resonance Raman study of the A-band short-time photodissociation dynamics of 2-iodothiophene

Resonance Raman spectra were obtained for 2-iodothiophene in cyclohexane solution with excitation wavelengths in resonance with the A-band absorption spectrum. These resonance Raman spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion mainly along the nominal symmetric C=C stretch of the thienyl ring and accompanied by a moderate amount of motion along the nominal symmetric CSC stretch, the nominal antisymmetric CSC stretch, and the nominal C-I stretch vibrational modes. A preliminary resonance Raman intensity analysis was done for the A-band resonance Raman spectra of 2-iodothiophene. These results were compared to previous results for related iodobenzene and iodoalkane molecules that also contain a C-I chromophore and the similarities and differences in the short-time photodissociation dynamics were discussed.     

Resonance Raman and theoretical investigation of the photodissociation dynamics of benzamide in S3 state

Resonance Raman spectra were obtained for benzamide in methanol and acetonitrile solutions with excitation wavelengths in resonance with the S(3) state. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with the motions mainly along the benzene ring C[Double Bond]C stretch nu(9), the Ph-CO-NH(2) and ring benzene stretch nu(14), the CCH in plane bend nu(17), the Ph-CO-NH(2) stretch and NH(2) rock nu(19), the ring trigonal bend nu(23), and the ring deformation and Ph-CO-NH(2) stretch nu(29). A preliminary resonance Raman intensity analysis was done, and the results were compared to those previously reported for acetophenone to examine the substituent effect. Solvent effect on the short-time photodissociation dynamics of benzamide was also examined. A conical intersection point S(2)S(3) between S(3) and S(2) potential energy surfaces of benzamide was determined by using a complete active space self-consistent field theory computations. The structural differences and similarities between S(3)S(2) point and S(0) were examined, and the results were used to correlate to the Franck-Condon photodissociation dynamics of benzamide in S(3) state.     

2-乙酰基-1-甲基吡咯激发态结构动力学及溶剂效应的共振拉曼光谱和密度泛函理论计算

获取了覆盖紫外光谱中A带和B带吸收的共7个不同激发波长的共振拉曼光谱, 并结合密度泛函理论方法研究了2-乙酰基-1-甲基吡咯(2-Ac-NMP)的A带和B带电子激发和Franck-Condon区域结构动力学. 在TD-B3LYP/6-311++G(d,p)计算水平上, A带和B带吸收的跃迁主体为π→π^* . A带和B带共振拉曼光谱分别指认为13个振动模式和8个振动模式的基频、泛频和组合频, 其中C＝O伸缩振动(ν₈)、C3-C4-C5不对称伸缩振动+C2-C6伸缩振动(ν₁₄)及环上CH面内摇摆(ν₁₈)对拉曼光谱强度贡献最大, 表明2-Ac-NMP的S_π激发态结构动力学主要沿反应坐标展开. 考察了溶剂对共振拉曼光谱强度模式的影响, 结果表明, 在同一溶剂中, 随激发波长由长变短, C＝O伸缩振动模(ν₈)的强度呈现出由强变弱再变强的现象. 这种变化规律与Franck-Condon区域S_n/S_π态混合或势能面交叉相关, 并受溶剂的有效调控.     

New perspectives on iron-ligand vibrations of oxyheme complexes

We report our studies of the vibrational dynamics of iron for three imidazole-ligated oxyheme derivatives that mimic the active sites of histidine-ligated heme proteins complexed with dioxygen. The experimental vibrational data are obtained from nuclear resonance vibrational spectroscopy (NRVS) measurements conducted on both powder samples and oriented single crystals, and which includes several in-plane (ip) and out-of-plane (oop) measurements. Vibrational spectral assignments have been made through a combination of the oriented sample spectra and predictions based on density functional theory (DFT) calculations. The two Fe-O(2) modes that have been previously observed by resonance Raman spectroscopy in heme proteins are clearly shown to be very strongly mixed and are not simply either a bending or stretching mode. In addition, a third Fe-O(2) mode, not previously reported, has been identified. The long-sought Fe-Im stretch, not observed in resonance Raman spectra, has been identified and compared with the frequencies observed for the analogous CO and NO species. The studies also suggest that the in-plane iron motion is anisotropic and is controlled by the orientation of the Fe-O(2) group and not sensitive to the in-plane Fe-N(p) bonds and/or imidazole orientations.     

Mode dependent vibrational autoionization of Rydberg states of NO2. II. Comparing the symmetric stretching and bending vibrations

Triple-resonance excitation and high-resolution photoelectron spectroscopy are combined to characterize the mode selectivity of vibrational autoionization of the high Rydberg states of NO2. Photoelectron spectra and vibrational branching fractions are reported for autoionizing Rydberg states converging to the NO2+ X 1Sigmag +(110) state, that is, with one quantum in the symmetric stretch, nu1, and one quantum in the bending vibration, nu2. These results indicate that autoionization proceeds most efficiently through the loss of one quantum from the symmetric stretch rather than from the bending vibration. The implications of this result are discussed in terms of the autoionization mechanism.     

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.     

Application of Fourier transform Raman spectroscopy to a range of compounds of pharmaceutical interest

Fourier transform (FT) Raman spectra have been obtained for a range of synthetic and semisynthetic samples to evaluate the utility of the technique for the characterization of compounds of pharmaceutical interest. These spectra are compared with the IR KBr disc spectra. Examples of the additional, important information which may be extracted from Raman data in comparison with IR spectroscopy are reported for the range of chemical structures studied. The superior ability of Raman to characterize the stretching modes of the CH bond compared with IR spectroscopy is demonstrated for several compounds.The characterization of highly symmetric vibrational modes is one of the most prominent and useful advantages of Raman spectroscopy and several examples of this primary application are also cited. These include the assignment of the ring breathing frequency of monosubstituted benzene rings, the CCC symmetric skeletal mode of a tricyclic fused ring system, the NO symmetric stretch of aromatic nitro groups and the stretching vibrations of various double bonds, several of which possess a high degree of local symmetry.     

N-甲基吡咯-2-甲醛激发态结构动力学及其溶剂效应的共振拉曼光谱和密度泛函理论研究

获取了覆盖N-甲基吡咯-2-甲醛(NMPCA)A-带和B-带电子吸收共7个激发波长的共振拉曼光谱,并结合含时密度泛函理论(TD-DFT)方法研究了的A-带和B-带电子激发和Franck-Condon区域结构动力学.TD-B3LYP/6-311++G(d,p)计算表明:A-带和B-带电子吸收的跃迁主体为π→π*.共振拉曼光谱可以指认为,11-13振动模式(A-带激发)或者7-11振动模式(B-带激发)的基频、倍频和组合频,其中C=O伸缩振动(ν7)、环的变形振动+N1-C6伸缩振动(ν17)、环的变形振动(ν21)和C6-N1-C2/C2-C3-C4不对称伸缩振动(ν14)占据了绝大部分.这表明NMPCA的Sπ激发态结构动力学主要沿C=O伸缩振动、环的变形振动和环上N1-C6伸缩振动等反应坐标展开.在同一溶剂的共振拉曼光谱中随激发波长由长变短,ν7与ν14的强度比呈现出由强变弱再变强的现象,这种变化规律被认为与Franck-Condon区域Sn/Sπ态混合或势能面交叉有关.溶剂对Sn/Sπ态混合或势能面交叉具有调控作用.     

3D Motions of Iron in Six‐Coordinate {FeNO}7 Hemes by Nuclear Resonance Vibration Spectroscopy

The vibrational spectrum of a six‐coordinate nitrosyl iron porphyrinate, monoclinic [Fe(TpFPP)(1‐MeIm)(NO)] (TpFPP=tetra‐para‐fluorophenylporphyrin; 1‐MeIm=1‐methylimidazole), has been studied by oriented single‐crystal nuclear resonance vibrational spectroscopy (NRVS). The crystal was oriented to give spectra perpendicular to the porphyrin plane and two in‐plane spectra perpendicular or parallel to the projection of the FeNO plane. These enable assignment of the FeNO bending and stretching modes. The measurements reveal that the two in‐plane spectra have substantial differences that result from the strongly bonded axial NO ligand. The direction of the in‐plane iron motion is found to be largely parallel and perpendicular to the projection of the bent FeNO on the porphyrin plane. The out‐of‐plane Fe‐N‐O stretching and bending modes are strongly mixed with each other, as well as with porphyrin ligand modes. The stretch is mixed with v₅₀ as was also observed for dioxygen complexes. The frequency of the assigned stretching mode of eight Fe‐X‐O (X=N, C, and O) complexes is correlated with the Fe?XO bond lengths. The nature of highest frequency band at ≈560 cm^?1 has also been examined in two additional new derivatives. Previously assigned as the Fe?NO stretch (by resonance Raman), it is better described as the bend, as the motion of the central nitrogen atom of the FeNO group is very large. There is significant mixing of this mode. The results emphasize the importance of mode mixing; the extent of mixing must be related to the peripheral phenyl substituents.     

Coherent Raman spectra of the nu1 mode of carbon suboxide

High-resolution (0.001 cm(-1)) coherent anti-Stokes Raman spectroscopy (CARS) has been used to study the nu1 symmetric CO stretching mode of the quasi-linear molecule carbon suboxide, C3O2. Q-branch transitions are seen that originate from the ground state and from thermally populated levels of the nu7 CCC bending mode, which is of unusually low frequency. The intensity variation of the Q-branch features on cooling to about 120 K in a jet expansion requires the reversal of the order of assignment given in a previous Raman study at low resolution. The identification of the nu1 sigma(g)+ <-- sigma(g)+ transition from the ground state is confirmed by the absence of J(odd) Q-branch lines in the resolved CARS spectrum. Analysis of this band in terms of a quasi-linear model gives a good fit to the observed transitions and leads to vibrational-rotational parameters (in cm(-1)) of nu1 = 2199.9773(12) and (B' - B') = -2.044(6) x 10(-4). Other transitions originating from higher nu7 levels occur at only slightly lower wavenumber values and permit the calculation of the double minimum potential in the Q7 bending coordinate. The results indicate that the ground-state barrier to linearity (21.5 cm(-1)) increases by only 0.6 cm(-1) when the CO symmetric stretch is excited.     

Symmetry properties of vibrational modes in mesoporphyrin IX dimethyl ester investigated by polarization-sensitive resonance Raman and CARS spectroscopy

The symmetry properties of selected vibrational modes of mesoporphyrin IX dimethyl ester (MP-IX-DME) in solution are investigated under different electronic resonance conditions. The Raman band parameters of the macrocycle modes nu(2), nu(10), nu(11), and nu(19) are determined from a quantitative analysis of polarized spontaneous resonance Raman (RR) and polarization-sensitive (PS) multiplex coherent anti-Stokes Raman scattering (CARS) spectra obtained with pre-resonant B band and resonant Qx band excitation, respectively. Additionally, the molecular geometry and the vibrational modes of MP-IX-DME are calculated by employing density functional theory (DFT) on the B3LYP/6-31G(d) level. Both the DFT-derived structure and the Raman spectroscopic parameters of MP-IX-DME indicate minor deviations from an ideal D2h macrocycle symmetry. To assess the influence of the beta substitution pattern on the in-plane symmetry, calculated normal-mode vectors and several experimentally detected parameters, such as peak positions, depolarization ratios, and coherent phases, are analyzed. The effects of the macrocycle substitution pattern are different for the selected vibrational modes: nu(2) in particular is very sensitive to subtle perturbations of the in-plane symmetry. The considerable activity of totally symmetric vibrations observed in the PS CARS spectra of MP-IX-DME and the correlation of mode symmetries with coherent phases confirm earlier PS CARS results on octaethylporphine (OEP) acquired under the same electronic resonance conditions.     

Resonance Raman spectroscopy and density functional theory calculation study of photodecay dynamics of tetra(4-carboxyphenyl) porphyrin

The 397.9 nm, 416.0 nm and 435.7 nm resonance Raman spectra were acquired for meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP) in tetrahydrofuran solution, and the Raman effect of relaxation dynamics was analyzed according to Herzberg-Teller (vibronic coupling) contributions. Density functional calculations were done to help the elucidation of the Soret (B(x) and B(y)-band) electronic transitions and the corresponding photo relaxation dynamics of TCPP. The spectra indicate that the Franck-Condon region photo relaxation dynamics upon S(0) → S(4) electronic transition are predominantly along the totally symmetric C(m)-ph stretch and Porphin ring breath stretch, and simultaneously along the asymmetric ν(C(m)-Phenyl) + δ(N-H) and ν(C(α)-C(m)-C(α))(as) + def (pyr) vibrational relaxation processes. The excited state structural dynamics of TCPP determined from the resonance Raman spectra show that the internal conversion between the B(y) and B(x) electronic states occurs in tens of femtoseconds, and the electronic relaxation dynamics were firstly interpreted taking into account the time-dependent wave packet theory and Herzberg-Teller (vibronic coupling) contributions.     

Quantum chemical calculation of infrared spectra of acidic groups in chabazite in the presence of water

The changes in the spectra of the acidic group in chabazite are studied by quantum chemical calculations. The zeolite is modeled by two clusters consisting of eight tetrahedral atoms arranged in a ring and seven tetrahedral atoms coordinated around the zeolite OH group. The potential energy and dipole surfaces were constructed from the zeolite OH stretch, in-plane and out-of-plane bending coordinates, and the intermolecular stretch coordinate that corresponds to a movement of the water molecule as a whole. Both the anharmonicities of the potential energy and dipole were taken into account by calculation of the frequencies and intensities. The matrix elements of the vibrational Hamiltonian were calculated within the discrete variable representation basis set. We have assigned the experimentally observed frequencies at approximately 2900, approximately 2400, and approximately 1700 cm(-1) to the strongly perturbed zeolite OH vibrations caused by the hydrogen bonding with the water molecule. The ABC triplet is a Fermi resonance of the zeolite OH stretch mode with the overtone of the in-plane bending (the A band) and the overtone of the out-of-plane bending (the C band). In the B band the stretch is also coupled with the second overtone of the out-of-plane bending. The frequencies at approximately 3700 and approximately 3550 cm(-1) we have assigned to the OH stretch frequencies of a slightly perturbed water molecule.     

Raman spectroscopic study of the tellurite minerals: rajite and denningite

Tellurites may be subdivided according to formula and structure. There are five groups based upon the formulae (a) A(XO3), (b) A(XO3).xH2O, (c) A2(XO3)3.xH2O, (d) A2(X2O5) and (e) A(X3O8). Raman spectroscopy has been used to study rajite and denningite, examples of group (d). Minerals of the tellurite group are porous zeolite-like materials. Raman bands for rajite observed at 740, and 676 and 667 cm(-1) are attributed to the nu1 (Te2O5)(2-) symmetric stretching mode and the nu3 (TeO3)(2-) antisymmetric stretching modes, respectively. A second rajite mineral sample provided a more complex Raman spectrum with Raman bands at 754 and 731 cm(-1) assigned to the nu1 (Te2O5)(2-) symmetric stretching modes and two bands at 652 and 603 cm(-1) are accounted for by the nu3 (Te2O5)(2-) antisymmetric stretching mode. The Raman spectrum of dennigite displays an intense band at 734 cm(-1) attributed to the nu1 (Te2O5)(2-) symmetric stretching mode with a second Raman band at 674 cm(-1) assigned to the nu3 (Te2O5)(2-) antisymmetric stretching mode. Raman bands for rajite, observed at (346, 370) and 438 cm(-1) are assigned to the (Te2O5)(2-)nu2 (A1) bending mode and nu4 (E) bending modes.     

Quantitative vibrational dynamics of iron in nitrosyl porphyrins

We use quantitative experimental and theoretical approaches to characterize the vibrational dynamics of the Fe atom in porphyrins designed to model heme protein active sites. Nuclear resonance vibrational spectroscopy (NRVS) yields frequencies, amplitudes, and directions for 57Fe vibrations in a series of ferrous nitrosyl porphyrins, which provide a benchmark for evaluation of quantum chemical vibrational calculations. Detailed normal mode predictions result from DFT calculations on ferrous nitrosyl tetraphenylporphyrin Fe(TPP)(NO), its cation [Fe(TPP)(NO)]+, and ferrous nitrosyl porphine Fe(P)(NO). Differing functionals lead to significant variability in the predicted Fe-NO bond length and frequency for Fe(TPP)(NO). Otherwise, quantitative comparison of calculated and measured Fe dynamics on an absolute scale reveals good overall agreement, suggesting that DFT calculations provide a reliable guide to the character of observed Fe vibrational modes. These include a series of modes involving Fe motion in the plane of the porphyrin, which are rarely identified using infrared and Raman spectroscopies. The NO binding geometry breaks the four-fold symmetry of the Fe environment, and the resulting frequency splittings of the in-plane modes predicted for Fe(TPP)(NO) agree with observations. In contrast to expectations of a simple three-body model, mode energy remains localized on the FeNO fragment for only two modes, an N-O stretch and a mode with mixed Fe-NO stretch and FeNO bend character. Bending of the FeNO unit also contributes to several of the in-plane modes, but no primary FeNO bending mode is identified for Fe(TPP)(NO). Vibrations associated with hindered rotation of the NO and heme doming are predicted at low frequencies, where Fe motion perpendicular to the heme is identified experimentally at 73 and 128 cm-1. Identification of the latter two modes is a crucial first step toward quantifying the reactive energetics of Fe porphyrins and heme proteins.     

Solvation of AlCl3 in deuterated acetonitrile studied by means of vibrational spectroscopy

Large blue shifts of the nu2 C=N stretch, nu4 Cz.sbnd;C stretch, and nu8 CCN deformation bands of CD3CN are observed in the infrared and Raman spectra of CD3CN solution of AlCl3, resulting from the donor-acceptor interactions of CD3CN with the Lewis acid. The Raman spectrum in the nu2 region shows further details; two new bands emerge on the blue side of the nu2 band of free CD3CN, and the ratio in intensity of the two bands also changes with concentration. Parallel to the nu2 region, similar new bands are observed on the blue sides of the nu4 and nu8 bands of free CD3CN. The solvation number of AlCl3, determined from the Raman intensities of the C=N stretch bands for free and coordinated CD3CN, increases from 1.54 to about 1.7 with decreasing concentration, indicating that various complexes with different numbers of coordinated acetonitrile coexist in the solution. The strong hydrogen bonds formed between the CD3 group and the chlorine atoms of the solute result in a large band appearing on the low frequency side of the nu1 CD3 symmetric stretch of free CD3CN.