Time, evolution, molecules with charge

Dielectric friction is the measure of the dynamic interaction of a charged or dipolar solute molecule with the surrounding polar solvent molecules. This concept has been applied, by Hynes et al. [339] and others [486], to solvent- and time-dependent fluorescence shifts resulting from the electronic absorption by a solute in polar solvents. If the solvent molecules are strongly coupled to the charge distribution in ground- and excited-state molecules, the relatively slow solvent reorientation can lead to an observable time evolution of the fluorescence spectrum in the nano- to picosecond range. This time-dependent fluorescence (TDF) has been theoretically analysed in terms of dynamic... 

These acceptor substitution effects on the nonlinear response of carotenoid have been studied extensively. Experimental investigations reveal that the substitution resulted in third-harmonic generation values up to 35 times higher than in /1-carotene which corresponds to N(ll) molecule. Subsequent CI/SOS quantum-chemical calculations rationalized the origin of this enhancement and assessed the applicability of simple models to describe the evolution of the molecular polarizabilities. In particular, this study shows a steplike increase of the longitudinal component of the dipole moment with the applied external field, caused by charge-transfer toward the acceptor end leading to an enhanced nonlinear response. 

The main goal of data treatment in conventional mass spectrometry (MS) is to facilitate identification and quantification of analytes. The focus of time-resolved mass spectrometry (TRMS) is to track variations of identities and quantities of analytes and products over time. In many chemical reactions, the concentrations of reactants decrease and those of products increase with time. In more complex reactions, reaction intermediates exist and their concentrations may increase and decrease within certain periods of time. The evolution of reaction intermediates is distinct from that of reactants and products. TRMS provides an insight into the progress of reactions by identifying molecules based on their mass-to-charge (m/z) ratios. It also determines concentrations of molecules based on signal intensities of ions. Thus, it is important for TRMS to interpret MS data on highly complex and dynamic systems correctly. This chapter will first introduce definitions of various technical terms, and then discuss how to predict molecular compositions of complex mixtures based on the information contained in mass spectra. 

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