Sum-frequency vibrational spectroscopy of centrosymmetric molecule at interfaces.

The centrosymmetric benzene molecule has zero first-order electric dipole hyperpolarizability, which results in no sum-frequency vibrational spectroscopy (SFVS) signal at interfaces, but it shows very strong SFVS experimentally. We perform a theoretical study on its SFVS, which is in good agreement with the experimental results. Its strong SFVS mainly comes from the interfacial electric quadrupole hyperpolarizability rather than the symmetry-breaking electric dipole, bulk electric quadrupole, and interfacial and bulk magnetic dipole hyperpolarizabilities, which provides a novel and completely unconventional point of view.

Sum-frequency vibrational spectroscopy of methanol at interfaces due to Fermi resonance.

Sum-frequency nonlinear spectroscopy is a powerful tool in investigating physical and chemical properties at gas/liquid, gas/solid, liquid/liquid and liquid/solid interfaces. Fermi resonance is a well-documented anharmonic phenomenon related to molecular vibrational coupling and the energy transfer phenomenon that exists within and between molecules. Such a phenomenon is widely used in the fields of materials, biology and chemistry. Combining density functional theory and molecular dynamics simulation, we present a method of studying sum-frequency vibrational spectroscopy for the CH3 group of methanol at interfaces due to Fermi resonance. The calculated spectroscopic data agree with the experiment and provide a novel and untraditional point of view with respect to traditional approaches.

Doubly Resonant Sum-Frequency Vibrational Spectroscopy of 1,1'-Bi-2-naphthol Chiral Solutions Due to the Nonadiabatic Effect.

Second-order nonlinear spectroscopy is a powerful tool in exploring significant physical and chemical characteristics at various interfaces and on chiral systems. We present a method of computing the nonadiabatic couplings between the different excited electronic states with time-dependent density functional theory and then study doubly resonant sum-frequency vibrational spectroscopy (SFVS) of chiral solutions due to the nonadiabatic, Franck-Condon, and Herzberg-Teller (HT) effects. The calculations for R-1,1'-bi-2-naphthol show that the theoretical spectra agree with experiment, and the nonadiabatic corrections are comparable with the HT terms or even larger for some vibrational modes, which is different from the mechanism of SFVS off electronic resonance. Doubly resonant SFVS may be a useful method of studying the nonradiative transition and nonadiabatic effect between the excited electronic states.

Theoretical Study on the Mechanism of the Acylate Reaction of ß-Lactamase.

Using density functional theory and a cluster approach, we study the reaction potential surface and compute Gibbs free energies for the acylate reaction of ß-lactamase with penicillin G, where the solvent effect is important and taken into consideration. Two reaction paths are investigated: one is a multi-step process with a rate-limit energy barrier of 19.1 kcal/mol, which is relatively small, and the reaction can easily occur; the other is a one-step process with a barrier of 45.0 kcal/mol, which is large and thus makes the reaction hard to occur. The reason why the two paths have different barriers is explained.

Herzberg-Teller Effect Predominates in Sum-Frequency Vibrational Spectroscopy of Limonene Chiral Liquids.

We theoretically study the bulk sum-frequency vibrational spectroscopy of chiral liquids under the influence of the Franck-Condon, Herzberg-Teller, and nonadiabatic effects. With quantum chemistry computations we calculate the chiral spectra for the R-limonene molecule. When we compare the theoretical and experimental spectra, we find that the Herzberg-Teller effect under the Born-Oppenheimer approximation, instead of the nonadiabatic effect, predominates in the chiral spectra.

Theoretical study on resonance Raman spectra of meso-tetrakis(3,5-di-tertiarybutylphenyl)-porphyrin due to the second-order Herzberg-Teller mechanism.

Using quantum chemistry computations TDDFT//B3LYP/6-31G(d), we study resonance Raman spectra of the Q band for meso-tetrakis(3,5-di-tertiarybutylphenyl)-porphyrin (H2TBPP) molecule due to the Franck-Condon and non-Condon mechanisms including the Herzberg-Teller and second-order Herzberg-Teller terms. Generally, the Herzberg-Teller terms are large. However, for some vibrational modes, the second-order Herzberg-Teller terms are the strongest and dominate resonance Raman spectra, which may also impact on fluorescence and absorption spectra. Hence, the Taylor expansion of the electric dipole transition moment with respect to the normal coordinates at the equilibrium structure of the ground electronic state may not converge for H2TBPP. A method to solve this problem is suggested.

Sum-frequency vibrational spectroscopy of limonene chiral liquids due to the nonadiabatic effect.

Using quantum computations we study sum-frequency vibrational spectroscopy of limonene chiral liquids due to the nonadiabatic effect in the non-resonant case for the first time. The nonadiabatic effect has an important impact on non-resonant antisymmetric polarizability and chiral sum-frequency vibrational spectroscopy. The theoretical spectroscopy agrees with the experimental spectroscopy. However, the nonadiabatic effect only has a small influence on non-resonant Raman. Bulk sum-frequency vibrational spectroscopy may become a powerful method of investigating the nonadiabatic effect and the nonradiative transition between excited electronic states for chiral molecules.

A theoretical study of sum-frequency generation for chiral solutions near electronic resonance.

We present a method of calculating sum-frequency generation (SFG) for chiral solutions near electronic resonance including the vibronic contributions, which give reasonable SFG intensities and show the Franck-Condon progressions for SFG. When studying R-1,1'-bi-2-naphthol (R-BN), we found that the calculated spectrum is in good agreement with the experimental one (Phys. Rev. Lett., 2001, 87, 113001). Then we apply this method to investigate SFG for chiral arabinose solutions. Theoretical results show that it may be difficult to observe the corresponding SFG even when the sum-frequency is exactly in resonance with the low-lying excited electronic states. Furthermore, we discuss the reason why SFG of chiral arabinose solutions is small.

Theoretical investigation of quadrupole contributions to surface sum-frequency vibrational spectroscopy.

We study the effect of electric transition quadrupole moments on surface sum-frequency vibrational spectroscopy (SFVS). The SSP, PPP and SPS effective sum-frequency susceptibilities are derived from the nonzero macroscopic susceptibility tensors and related to molecular quadrupole polarizabilities. Using time-dependent density functional theory, we calculate the quadrupole susceptibilities of R-limonene liquids for the first time. The results indicate that quadrupole contributions have a significant influence on SFVS transmitted signals in the SPS polarization combination. We also suggest that the SPS spectra may be used as a general technique for detecting electric transition quadrupole moments.

Theoretical study of the resonance Raman spectra for meso-tetrakis(3,5-di-tertiarybutylphenyl)-porphyrin.

Applying time-dependent density functional theory (TDDFT), we study the resonance Raman spectra for the Q and B bands of the meso-tetrakis(3,5-di-tertiarybutylphenyl)-porphyrin (H2TBPP) molecule including both Raman A term (Franck-Condon term) and Raman B term (Herzberg-Teller term) contributions. It is found that Raman B term can be one order of magnitude larger than Raman A term and dominates resonance Raman for the Q band resonance. In comparison with the recent experimental Raman spectra of H2TBPP with incident light frequency 532nm, we predict the absence of 1580cm(-1) band in the resonance Raman spectra which agrees well with the experimental results, whereas the previous theoretical calculation using non-resonance strategy failed to do so.

Theoretical study of sum-frequency vibrational spectroscopy on limonene surface.

By combining molecule dynamics (MD) simulation and quantum chemistry computation, we calculate the surface sum-frequency vibrational spectroscopy (SFVS) of R-limonene molecules at the gas-liquid interface for SSP, PPP, and SPS polarization combinations. The distributions of the Euler angles are obtained using MD simulation, the ψ-distribution is between isotropic and Gaussian. Instead of the MD distributions, different analytical distributions such as the δ-function, Gaussian and isotropic distributions are applied to simulate surface SFVS. We find that different distributions significantly affect the absolute SFVS intensity and also influence on relative SFVS intensity, and the δ-function distribution should be used with caution when the orientation distribution is broad. Furthermore, the reason that the SPS signal is weak in reflected arrangement is discussed.

Ozone dissociation to oxygen affected by Criegee intermediate.

The detailed potential energy surfaces for the reactions of Criegee intermediate (CI, H2COO) and formaldehyde (H2CO) with ozone (O3) have been investigated at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311++G(2d,2p) level of theory, respectively. New alternative reaction mechanisms, to the one previously proposed (J. Phys. Chem. Lett. 2013, 4, 2525) have been found. The lower barrier of the new mechanism shows that it is easy for H2COO + O3 to dissociate to formaldehyde and oxygen. For the reactions of H2CO with O3 to produce H2COO and O2, we find relatively high energy barriers, which makes the ozone dissociation to oxygen unlikely to be catalyzed by CI.

Theoretical study of doubly resonant IR-UV hyper-Raman scattering.

Theoretically we study the doubly resonant IR-UV hyper-Raman scattering where the IR light is resonant to the vibrational transition and the UV/visible light is resonant to the electronic transition between the ground and excited states. Based on the Taylor expansion of the electric transition dipole moments with respect to the normal coordinates, we have derived the expressions for the hyper-Raman A, B, and C terms. Using quantum chemistry calculations, we have estimated the magnitudes for all the three terms. Due to double resonance, contributions from all the three terms should be detectable in experiments.

Density functional theory study on sum-frequency vibrational spectroscopy of arabinose chiral solutions.

Using time-dependent density functional computations we calculate the doubly resonant IR-UV sum-frequency vibrational spectroscopy and sum-frequency vibrational spectroscopy off electronic resonance for D-arabinose solutions. In comparison with the experimental detection limit, the calculated doubly resonant IR-UV sum-frequency vibrational spectroscopy is strong enough to be detectable.

Density functional theory study on anti-resonance in preresonance Raman scattering for naphthalene molecules.

The anti-resonance phenomenon in preresonance Raman scattering is investigated on the basis of the direct Taylor expansion of the electric dipole transition moments in vibrational Raman tensors with respect to vibrational normal coordinates. A time-dependent density functional theory treatment is applied to compute the anti-resonance of a nontotally symmetric vibrational model for naphthalene molecules, and the model spectra agree favorably with experiment. This direct evaluation approach may provide a method of predicting anti-resonance and studying its origin.

Theoretical study of sum-frequency vibrational spectroscopy off electronic resonance on limonene chiral liquids.

The sum-frequency vibrational spectroscopy (SFVS) off electronic resonance on chiral liquids is analyzed using the approach of antisymmetric nonresonant vibrational Raman scattering tensor calculation, which is based on the direct Taylor expansion of electronic transition moments in vibrational normal coordinates. A single-excitation configuration interaction treatment is applied to compute the SFVS off electronic resonance for (R)-limonene molecules, and the model spectra compare favorably with experimental data. This direct evaluation approach may provide a method of computing antisymmetric nonresonant vibrational Raman polarizabilities and predicting and assigning the SFVS off electronic resonance on chiral liquids.

Ab initio/density functional theory and multichannel RRKM study for the ClO + CH2O reaction.

The potential energy surface for the CH(2)O + ClO reaction was calculated at the QCISD(T)/6-311G(2d,2p)//B3LYP/6-311G(d,p) level of theory. The rate constants for the lower barrier reaction channels producing HOCl + HCO, H atom, OCH(2)OCl, cis-HC(O)OCl and trans-HC(O)OCl have been calculated by TST and multichannel RRKM theory. Over the temperature range of 200-2000 K, the overall rate constants were k(200-2000K) = 1.19 x 10(-13)T(0.79) exp(-3000.00/T). At 250 K, the calculated overall rate constant was 5.80 x 10(-17) cm(3) molecule(-1) s(-1), which was in good agreement with the experimental upper limit data. The calculated results demonstrated that the formation of HOCl + HCO was the dominant reaction channel and was exothermic by 9.7 kcal/mol with a barrier of 5.0 kcal/mol. When it retrograded to the reactants CH(2)O + ClO, an energy barrier of 14.7 kcal/mol is required. Furthermore, when HOCl decomposed into H + ClO, the energy required was 93.3 kcal/mol. These results suggest that the decomposition in both the forward and backward directions for HOCl would be difficult in the ground electronic state.

Rotationally resolved optical rotation and circular dichroism effects for symmetric top molecules induced by a resonant circularly polarized pumping optical field.

The rotationally resolved laser-induced optical activity including the laser-induced optical rotation (LIOR) and laser-induced circular dichroism (LICD) effects of an IR probing light pumped by a collinear intense resonant circularly polarized light dependent on the third-order susceptibility due to the pure electric dipole interaction for achiral symmetric top molecules in the gas phase is discussed theoretically. The laser-induced optical activity contains four distinct contributions named A, B, C, and D terms: the B term of the LIOR and LICD arising from the rotational wave function perturbed by the pumping light is deduced using the semiclassical perturbation theory, and the expressions for A, C, and D terms, respectively, due to the ac Stark effect, the Boltzmann statistical redistribution, and the alteration of occupation polability, are obtained from previous results [Zheng, R.-H.; Chen, D.-M.; Wei, W.-M.; He, T.-J.; Liu, F.-C. J. Chem. Phys. 2004, 121, 6835]. The microwave-IR double resonant spectrum is proposed to detect the LIOR and LICD effects. As an example, the LIOR and LICD for the HCF(3) molecules in the conditions of 298.15 K and 0.3 Torr when the IR probing light sweeps over the rotational-vibrational transition of the v(5) and v(1) modes and the right circularly polarized microwave pumping light with the intensity of 1 kW cm(-2) at the resonant frequency 40.84 GHz are calculated on the basis of the B3LYP/6-311++G* computations. The theoretical results indicate that the B term can be of the same order of magnitude as the A and D terms, and the LIOR and LICD can be measurable in comparison to the rotationally resolved MVCD. The laser-induced optical activity may provide useful new information and form a basis for a different kind of optical activity spectroscopy.

Theoretical investigation of doubly resonant IR-UV sum-frequency vibrational spectroscopy of binaphthol chiral solution.

The doubly resonant IR-UV sum-frequency vibrational spectroscopy (SFVS) of 1,1'-bi-2-naphthol (BN) solution and its dispersion spectra are analyzed and computed using the ZINDO//AM1 calculation and the direct approach of Raman scattering tensor calculation, which is based on calculations of Franck-Condon factors and on differentiation of the electronic transition moments with respect to the vibrational normal modes. The calculated results indicate that, for the most intense vibrational bands observed in the SFVS experiment, the calculated frequencies, symmetry, order, intensities, and pattern of the enhanced vibrational modes agree with experiment qualitatively, and due to the Franck-Condon progression, there are the doublet peaks in the corresponding resonant sum-frequency dispersion spectra. The polarization resonance Raman spectra of BN for the vibrational modes appearing in SFVS are also computed and associated with the experiment SFVS of BN. This direct evaluation approach of Raman tensors may provide a way of assigning the doubly resonant IR-UV SFVS.