Solvation Effects in Four‐Wave Mixing and Spontaneous Raman and Fluorescence Lineshapes of Polyatomic Molecules

Mukamel, Shaul

doi:10.1002/9780470141199.ch6

Cited by 70 publications

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“…A theory of the resonance Raman effect based on vibrational wavepackets was developed by Heller, Mathies, Meyers and their colleagues [6][7][8][9][10][11]. Mukamel [1,12] presented a comprehensive theory that considered the nonlinear response functions for pathways in Liouville space. Having briefly described the pertinent pathways in Liouville space above, we will first develop the Kramers-Heisenberg-Dirac theory by a second-order perturbation approach, and then turn to the wavepacket picture.…”

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Raman Scattering and Other Multi-photon Processes

Parson

2015

Modern Optical Spectroscopy

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The vibrational transitions discussed in Chap. 6 occur by absorption of a photon whose energy matches a vibrational energy spacing, hυ. Vibrational or rotational transitions also can occur when a molecule scatters light of higher frequencies; this is the phenomenon of Raman scattering. Raman scattering is one of a group of two-photon processes in which one photon is absorbed and another is emitted essentially simultaneously. Figure 12.1 illustrates the main possibilities. Rayleigh scattering is an elastic process, in which there is no net transfer of energy between the molecule and the radiation field: the incident and emitted photons have the same energy ( Fig. 12.1, transition A). Raman scattering is an inelastic process in which the incident and departing photons differ in energy and the molecule is either promoted to a higher vibrational or rotational level of the ground electronic state, or demoted to a lower level. Raman transitions in which the molecule gains vibrational or rotational energy, called Stokes Raman scattering (Fig. 12.1, transition B), usually predominate over transitions in which energy is lost (anti-Stokes Raman scattering, Fig. 12.1, transition C) because resting molecules populate mainly the lowest levels of any vibrational modes with hυ > k B T. The strength of anti-Stokes scattering increases with temperature, and the ratio of anti-Stokes to Stokes scattering provides a way to measure the effective temperature of a molecule. Both Stokes and anti-Stokes Raman scattering increase greatly in strength if the incident light falls within a molecular absorption band (Fig. 12.1, transition D). The scattering then is termed resonance Raman scattering.There are other types of light scattering that involve transfer of different forms of energy between the molecule and the radiation field. In Brillouin scattering, the energy difference between the absorbed and emitted photons creates acoustical waves in the sample; in quasielastic or dynamic light scattering, the energy goes into small changes in velocity or rotation. In two-photon absorption, the second photon is absorbed rather than emitted, leaving the molecule in a excited electronic state whose energy is the sum of the energies of the two photons. 513Raman scattering was discovered in 1928 by the Indian physicist C.V. Raman. It usually is measured by irradiating a sample with a narrow spectral line from a continuous laser, but time-resolved measurements also can be made by using a pulsed laser as the light source. Light scattered at 90 or another convenient angle from the axis of incidence is collected through a monochromator, and the intensity of the signal is plotted as a function of the diference in frequency or wavenumber between the excitation light and the scattered photons (v e À v s ). The spectrum resembles an IR absorption spectrum ( Fig. 12.2). However, the relative intensities of the Raman and IR lines corresponding to various vibrational modes generally differ, as we will discuss below. Resonance Raman spectra of macromolecules a...

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