V Workshop em Fı́sica Molecular e Espectroscopia
AMB − Painel − 27
Study of the first hyperpolarizability in aminophenol molecules
N. M. Barbosa Neto (1), A. E. H. Machado (2), L. T. Ueno (2), J. M. Madurro (2), A. G. Brito-Madurro (2), P. L.
FRanzen (3), S. C. Zilio (3)
(1) Instituto de Fı́sica - Universidade Federal de Uberlândia
(2) Instituto de Quı́mica - Universidade Federal de Uberlândia
(3) Instituto de Fı́sica de São Carlos - Universidade de São Paulo
In this work we report on the study of the first hyper-polarizability (β), obtained with a new extension of hyper-Rayleigh
scattering technique, named pulse trains hyper-Rayleigh scattering (PTHRS). This extension allows improved and fast
measurements, once mechanical actions to vary the pulse intensity can be eliminated and high frequency rates can
be used to acquire large statistics in short time. In PTHRS, the sample is pumped by the fundamental harmonic of
a solid state Nd:YAG laser. Laser delivered mode-locked and Q-switched pulse trains with approximately 20 pulses
of 70 ps separated by 13 ns. Two crossed polarizers were used to limit the laser intensity. We have obtained the
first hyper-polarizability for aminophenols as function of the N H2 group position. We observed a clear dependence
between N H2 position and β value, with ortho-aminophenol presenting the higher first hyper-polarizability. In order to
corroborate our results we performed quantum chemical calculations to obtain the Mulliken distribution charge and static
first hyper-polarizability (β(0)). The theoretical static β were corrected to consider the resonance enhancement effect.
The methodology adopted in quantum chemical calculations consisted of two steps: (i) the ground state geometry
optimization and Mulliken charge distribution, for all molecules, were obtained via Hartree-Fock implemented in
Gaussian program. The Gaussian keywords used in geometry optimization were: apolar, MPG, MPGCRT = 0.001. (ii)
The β(0) was calculated through AM1 method implemented in AMPAC program. Although, quantitative discrepancies
are observed between experimental and theoretical results, which can be possible caused by the no consideration of
external factors during the calculation (e.g. solvent effect), a excellent agreement is obtained in the ratio between
the β values for different isomers. This fact indicates that the theoretical approach used is very adequate to predict
modification in the first hyperpolarizability as function of molecular modifications.