|
Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
| ABSTRACT - Internet Electron. J. Mol. Des. June 2005, Volume 4, Number 6, 423-433 |
Changes in Dipole Moments and Polarization of a Two-Level System with Intramolecular Coupling
José Luis Paz and Teresa Cusati
Internet Electron. J. Mol. Des. 2005, 4, 423-433
|
Abstract:
Polyatomic molecules can be described by a two-level system
represented by two crossed harmonic potential curves (including
vibrational levels) in order to study their nonlinear signal response.
The variation of the coupling parameter has an important influence
on the behavior of the dipole moments and, consequently, on the
polarization on the new coupled-state basis. The calculation
method employed is based on the Liouville formalism for the
density matrix, where the conventional optical Bloch equations
are solved in Fourier space to obtain the density matrix elements
associated to the polarization of the system. Changes in the
coupling parameters V0 (energetic difference between the minima
of the potential curves), S (height to which the vibronic coupling
occurs) and v (coupling parameter) produce modifications in the
behavior of the dipole moments and polarization on the coupled
system. In this communication, two studies are presented: (a)
variation of the parameters S and v,
while keeping V0 constant and,
(b) variation of S and V0,
while keeping v constant. In order to study
the effects of these changes, the rotating-wave approximation is
neglected, which permits us to analyze the processes that occur out
of the resonance region. Moreover, the permanent dipole moments
of the states in the uncoupled basis are included. First case
(variation of S and v): an important increment of dipole moments
and polarization magnitude values were observed for low values of
v and high values of S. Second case
(variation of S and V0): an
abruptly increment in the polarization magnitude were found at
high values of S and low values of V0.
The observed changes in the
nonlinear response are associated to modifications in the overlap
integral and consequently to the dipole moments of the states in the
new coupled basis.
|