Light molecular response

Quantum-mechanical expressions for the polarizability and other higher-order molecular response tensors are obtained by taking expectation values of the operator equivalent of the electric dipole moment (2.5) using molecular wavefunctions perturbed by the light wave (2.4). This particular semi-classical approach avoids the complications of formal time-dependent perturbation theory it has a respectable pedigree, being found in Placzek s famous treatise on the Raman effect [9], and also in the books by Born and Huang [lO] and Davydov [ll]. Further details of the particular version outlined here can be found in my own book [12]. 

Brumer P, Shapiro M (2012) Molecular response in one-photon absorption via natural thermal light vs. pulsed laser excitation. Proc Natl Acad Sd USA 109 19575... 

Chromophores and their light-induced molecular response... 

The protonated Schiff base of 11-cis-retinal (PSBll) is the chromophore in the visual receptor rhodopsin. A light-induced cisitrans isomerization of the chromophore triggers the primary event in vision, which is a series of conformational changes of the protein. This photoreaction is considered as the archetype of a chemical reaction optimized by nature to achieve a specific molecular response. Hence, it was in focus of numerous computational and experimental investigations. 

DIRLD spectroscopy belongs to the characterization techniques known as Vheo-optics. Rheo-optical analysis of materials utilizes electromagnetic probes in conjunction with application of macroscopic mechanical perturbations. It investigates primarily the microscopic or molecular responses of materials under deformation, flow, and relaxation. In dynamic rheo-optical methods, such as dynamic birefringence, light scattering, and X-ray diffraction, relationships... 

Radiation probes such as neutrons, x-rays and visible light are used to see the structure of physical systems tlirough elastic scattering experunents. Inelastic scattering experiments measure both the structural and dynamical correlations that exist in a physical system. For a system which is in thennodynamic equilibrium, the molecular dynamics create spatio-temporal correlations which are the manifestation of themial fluctuations around the equilibrium state. For a condensed phase system, dynamical correlations are intimately linked to its structure. For systems in equilibrium, linear response tiieory is an appropriate framework to use to inquire on the spatio-temporal correlations resulting from thennodynamic fluctuations. Appropriate response and correlation functions emerge naturally in this framework, and the role of theory is to understand these correlation fiinctions from first principles. This is the subject of section A3.3.2. 

The dye is excited by light suppHed through the optical fiber (see Fiber optics), and its fluorescence monitored, also via the optical fiber. Because molecular oxygen, O2, quenches the fluorescence of the dyes employed, the iatensity of the fluorescence is related to the concentration of O2 at the surface of the optical fiber. Any glucose present ia the test solution reduces the local O2 concentration because of the immobilized enzyme resulting ia an iacrease ia fluorescence iatensity. This biosensor has a detection limit for glucose of approximately 100 ]lM , response times are on the order of a miaute. 

From careful measurements of such processs, it is possible to develop quantitative models to describe the molecular dynamical response to impulsive laser excitation. These enable the fundamental interaction of intense, ultrafast laser light with molecules to be understood from first... 

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