Chemically induced dynamic time dependence

In order to study the viscosity effect on the quenching of triplet excited state of (53) by TEMPO, chemically induced dynamic electron polarization and transient absorption spectra have been measured in ethylene glycol, 1,2-propanol and their mixtures. The results indicate that the quenching rate constant is viscosity-dependent and decreases linearly with the increase in solvent viscosity. The spectroscopy and dynamics of near-threshold excited states of the isolated chloranil radical anion have been studied using photoelectron imaging taken at 480 nm, which clearly indicates resonance-enhanced photodetachment via a bound electronic excited state. Time-resolved photoelectron imaging reveals that the excited state rapidly decays on a timescale of 130 fs via internal conversion. ... 

The general experimental approach used in 2D correlation spectroscopy is based on the detection of dynamic variations of spectroscopic signals induced by an external perturbation (Figure 7.43). Various molecular-level excitations may be induced by electrical, thermal, magnetic, chemical, acoustic, or mechanical stimulations. The effect of perturbation-induced changes in the local molecular environment may be manifested by time-dependent fluctuations of various spectra representing the system. Such transient fluctuations of spectra are referred to as dynamic spectra of the system. Apart from time, other physical variables in a generalised 2D correlation analysis may be temperature, pressure, age, composition, or even concentration. 

The Time Dependent Processes Section uses time-dependent perturbation theory, combined with the classical electric and magnetic fields that arise due to the interaction of photons with the nuclei and electrons of a molecule, to derive expressions for the rates of transitions among atomic or molecular electronic, vibrational, and rotational states induced by photon absorption or emission. Sources of line broadening and time correlation function treatments of absorption lineshapes are briefly introduced. Finally, transitions induced by collisions rather than by electromagnetic fields are briefly treated to provide an introduction to the subject of theoretical chemical dynamics. 

In 2D-1R spectroscopy, the sample is perturbed externally to induce time-dependent fluctuations of the IR signal. The external perturbation can be any perturbation source that can excite chemical species in the system, including mechanical, optical, electrical, magnetic, chemical, thermal and acoustic perturbations. The reorientation of each functional group in the sample with a unique rate, extent, and direction produces resolvable fluctuations in the dynamic IR intensities. The changes are recorded in the dynamic spectra in the form of variation in the intensities, shifts of spectral band positions and changes in the shape of peaks. 

The basic scheme adapted for generating 2D IR spectra [3, 8] is shown in Figure 1-2. In a typical optical spectroscopy experiment, an electromagnetic probe (e.g., IR, X-ray, UV or visible light) is applied to the system of interest, and physical or chemical information about the system is obtained in the form of a spectrum representing a characteristic transformation (e.g., absorption, retardation, and scattering) of the electromagnetic probe by the system constituents. In a 2D IR experiment, an external physical perturbation is applied to the system [2, 3] with the incident IR beam used as a probe for spectroscopic observation. Such a perturbation often induces time-dependent fluctuations of the spectral intensity, toown as the dynamic spectrum, superposed onto the normal static IR spectrum. 

As a fundamental study on field induced chemical reactions, Neidel and Vrakking et al. observed attosecond d3mamics of electrons in a series of small- and medium sized neutral molecules by monitoring time-dependent variation of the parent molecular ion 3delds [296]. The information on electron dynamics was extracted from experimental data on the basis of the relation between the time dependent dipole and ionization. This was performed in the two-color femtosecond near infrared (NIR) pump-attosecond extreme ultraviolet (XUV) probe experiment. They claim that the time-dependent dipole induced by the moderately strong NIR pulse field is monitored with attosecond time resolution. The oscillations are interpreted in terms of a time dependent screening induced by the polarization of the molecule, which alters the photoionization yield of the neutral molecule. This scheme can be considered as the first example of molecular attosecond Stark spectroscopy. 

Abstract We present a general theoretical approach for the simulation and control of ultrafast processes in complex molecular systems. It is based on the combination of quantum chemical nonadiabatic dynamics on the fly with the Wigner distribution approach for simulation and control of laser-induced ultrafast processes. Specifically, we have developed a procedure for the nonadiabatic dynamics in the framework of time-dependent density functional theory using localized basis sets, which is applicable to a large class of molecules and clusters. This has been combined with our general approach for the simulation of time-resolved photoelectron spectra that represents a powerful tool to identify the mechanism of nonadiabatic processes, which has been illustrated on the example of ultrafast photodynamics of furan. Furthermore, we present our field-induced surface hopping (FISH) method which allows to include laser fields directly into the nonadiabatic... 

Figure 33 illustrates the schematic set up for a DIRLD spectroscopy experiment. A small-amplitude oscillatory tensile strain is applied to a sample, and the time-dependent fluctuations of IR dichroism signals corresponding to the dynamic reorientations of electric dipole transition moments associated with the molecular vibrations of various constituent chemical groups of the system induced by the applied strain are monitored with a pair of polarized IR beams oriented in directions parallel and perpendicular to the strain direction. Under a small-amplitude dynamic strain, the time-dependent dichroic difference can also be treated as the sum of a quasistatic component AA(v) and a dynamic component AA(v, t) induced by the strain s(t), similar to the stress response described in eqn [25]. 

---