Nonlinear vibrational spectroscopic

Kim et al. [22] have used vibrational sum-frequency generation spectroscopy (SFG) to characterize the surfaces of (3-HMX single crystals, as well as the interface between HMX and the copolymer Estane. SFG is a nonlinear vibrational spectroscopic technique, related to optical parametric amplification that selectively probes vibrational transitions at surfaces and interfaces. Compared with bulk HMX, the surface vibrational features are blueshifted and observed splittings are larger. The technique may have application to detection of explosive residues on surfaces. 

Nonlinear Vibrational Spectroscopic Microscopy of Cells and Tissue... 

In order to realize molecular-vibration spectroscopy, coherent anti-Stokes Raman scattering (CARS) spectroscopy is employed, which is one of the most widely used nonlinear Raman spectroscopes (Shen 1984). CARS spectroscopy uses three incident fields including a pump field (< i), a Stokes field (0)2, 0 2 < 1) and a probe field (<0/ = <0i), and induces a nonlinear polarization at the frequency of <03 = 2<0i - <02 which is given in a scalar form by... 

In this section we present theoretical and experimental demonstrations of a vibrational spectroscopic technique, vibrational echo spectroscopy (VES) (54,55). The VES technique can generate a vibrational transition spectrum with background suppression using the nonlinear vibrational echo pulse sequence. In contrast to the previous results, VES is a utilization of vibrational echoes to measure spectra rather than dynamics. In a standard vibrational echo experiment, the wavelength of the IR light is fixed, and the delay, r, between the excitation pulses is scanned. In VES, r is fixed and the wavelength is scanned. 

We have presented two types of nonlinear IR spectroscopic techniques sensitive to the structure and dynamics of peptides and proteins. While the 2D-IR spectra described in this section have been interpreted in terms of the static structure of the peptide, the first approach (i.e., the stimulated photon echo experiments of test molecules bound to enzymes) is less direct in that it measures the influence of the fluctuating surroundings (i.e., the peptide) on the vibrational frequency of a test molecule, rather than the fluctuations of the peptide backbone itself. Ultimately, one would like to combine both concepts and measure spectral diffusion processes of the amide I band directly. Since it is the geometry of the peptide groups with respect to each other that is responsible for the formation of the amide I excitation band, its spectral diffusion is directly related to structural fluctuations of the peptide backbone itself. A first step to measuring the structural dynamics of the peptide backbone is to measure stimulated photon echoes experiments on the amide I band (51). 

Vapor pressure experiments and vibrational spectroscopic studies " show that SeCl2 and SeBt2 exist as dissociation products of the corresponding tetrahalides in the vapor phase or in organic solvents, or as mixtures of Se02 and Se in aqueous HCl. Their nonlinear structures were determined by photoelectron spectra and by electron diffraction. " ... 

A nonlinear molecule of N atoms has 32V — 6 internal vibrational degrees of freedom, and therefore 3A — 6 normal modes of vibration (the three translational and three rotational degrees of freedom are not of vibrational spectroscopic relevance). Thus, there are 32V — 6 independent internal coordinates, each of which can be expressed in terms of Cartesian coordinates. To first order, we can write any internal displacement coordinate ry in the form... 

Figure 7.1 Energy level transitions for different vibrational spectroscopic techniques infrared absorption. SFG nonlinear spectroscopy. Raman and HREELS iwhere an electron is inelastically scattered .

Abstract. The development of modern spectroscopic techniques and efficient computational methods have allowed a detailed investigation of highly excited vibrational states of small polyatomic molecules. As excitation energy increases, molecular motion becomes chaotic and nonlinear techniques can be applied to their analysis. The corresponding spectra get also complicated, but some interesting low resolution features can be understood simply in terms of classical periodic motions. In this chapter we describe some techniques to systematically construct quantum wave functions localized on specific periodic orbits, and analyze their main characteristics. 

In this chapter, we showed the capability of near-field optical spectroscopy combined with vibrational spectroscopy and nonlinear optics for biochemical applications. The evanescent field localized at the nanoscale tip realized the extremely small light source for various spectroscopes in the near-field. Especially when the tip is made... 

INTRODUCTION. A standard and universal description of various nonlinear spectroscopic techniques can be given in terms of the optical response functions (RFs) [1], These functions allow one to perturbatively calculate the nonlinear response of a material system to external time-dependent fields. Normally, one assumes that the Born-Oppenheimer approximation is adequate and it is sufficient to consider the ground and a certain excited electronic state of the system, which are coupled via the laser fields. One then can model the ground and excited state Hamiltonians via a collection of vibrational modes, which are usually assumed to be harmonic. The conventional damped oscillator is thus the standard model in this case [1]. 

In our discussion the usual Born-Oppenheimer (BO) approximation will be employed. This means that we assume a standard partition of the effective Hamiltonian into an electronic and a nuclear part, as well as the factorization of the solute wavefunction into an electronic and a nuclear component. As will be clear soon, the corresponding electronic problem is the main source of specificities of QM continuum models, due to the nonlinearity of the effective electronic Hamiltonian of the solute. The QM nuclear problem, whose solution gives information on solvent effects on the nuclear structure (geometry) and properties, has less specific aspects, with respect the case of the isolated molecules. In fact, once the proper potential energy surfaces are obtained from the solution of the electronic problem, such a problem can be solved using the standard methods and approximations (mechanical harmonicity, and anharmonicity of various order) used for isolated molecules. The QM nuclear problem is mainly connected with the vibrational properties of the nuclei and the corresponding spectroscopic observables, and it will be considered in more detail in the contributions in the book dedicated to the vibrational spectroscopies (IR/Raman). This contribution will be focused on the QM electronic problem. 

To perform the VES calculations it is necessary to consider a finite duration pulse, which has a finite bandwidth. In addition, the actual shape of the vibrational echo spectrum depends on the bandwidth of the laser pulse and the spectroscopic line shape. Several species with different concentrations, transition dipole moments, line shapes, and homogeneous dephasing times can contribute to the signal. Therefore, VES calculations require determination of the nonlinear polarization using procedures that can accommodate these properties of real systems. 

The ability to rephase inhomogeneity in Raman-active intermolecular vibrations was increased with the use of five-order spectroscopic technique (Tanamura and Mukamel, 1993 Mukamel, 2000 Fourkas, 2001). Five-order spectroscopy relies on the existence of some sorts of nonlinearity, either in the coordinate dependence of polarizability or in... 

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