Theory of resonance emission: Microscopic origins of stochastic modulation

Journal Article · Tue Sep 15 04:00:00 EDT 1981 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.442411· OSTI ID:6213813

Rhodes, W

The nature of resonance emission of light, which appears as a mixture of (coherent) resonance scattering and (incoherent) resonance fluorescence, is considered. The basic conceptual elements which distinguish the scattering and fluorescence components for the linear excitation limit are developed in terms of a simple formulation whereby a molecule interacts with a coherent Lorentzian light pulse which increases exponentially with time for t<0 and is turned off at t = 0. These results together with the ideas, currently existing in the literature, that stochastic modulation of a molecule by its medium is essential for the appearance of fluorescence provide the basis for the further formulation of a theory which does not require the ad hoc introduction of a random potential. The theory developed considers the microscopic origins of manifest stochastic modulation effects in terms of a bath potential for the molecule--medium (bath) degrees of freedom. This potential, termed the sudden potential, is associated with the change in interaction with the medium that a molecule experiences upon intramolecular state transitions which are induced by external interactions (e.g., by light). Development of the reduced molecule--field density operator leads naturally to a separation of terms which describes scattering and (the propensity for) fluorescence. Critical to the theory is a four-time correlation function for the bath (sudden) potential. The difficulties inherent in defining absorption (spectrum) resonances and the corresponding distinctions between resonance and relaxed emission are discussed. Implications are considered for the further understanding of experimental results on molecular excitation dynamics in the gas phase and in supersonic jets. Sources of stochastic modulation other than material media are mentioned.

• Research Organization: Department of Chemistry and Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306
• OSTI ID: 6213813
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 75:6; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640305* -- Atomic
Molecular &amp; Chemical Physics-- Atomic &amp; Molecular Theory-- (-1987)
74 ATOMIC AND MOLECULAR PHYSICS
COHERENT RADIATION
COLLISIONS
ELECTROMAGNETIC FIELDS
ELECTROMAGNETIC RADIATION
EMISSION SPECTRA
FLUORESCENCE
INELASTIC SCATTERING
LIGHT SCATTERING
LUMINESCENCE
MOLECULE COLLISIONS
MOLECULES
PHOTON COLLISIONS
PHOTON-MOLECULE COLLISIONS
RADIATIONS
RESONANCE SCATTERING
SCATTERING
SPECTRA
STOCHASTIC PROCESSES