Mary C. Salazar

Intramolecular coupling study of the resonances in the four-wave mixing signal

Abstract The effect of the intramolecular coupling on the resonances associated to the Four-wave mixing signal is studied in the present contribution. The transition and permanent dipole moments are critical quantities for this analysis of the local macroscopic polarization in the adiabatic representation when the rotating wave approximation is not considered. New characteristics of the resonance, emerging as a consequence of the vibronic coupling, are studied here in the framework of a local homogeneous-linewidth third-order perturbation model.

Cavity ring down absorption at low temperatures: C–H spectra (Δυ = 1–6) of CH3D and C–H overtones (Δυ = 5, 6) of CH2D2 and CH4

The spectra of the C–H stretch fundamental and overtones (Δυ = 1–6) of CH3D have been recorded. Absorptions in the visible were obtained with a phase shift cavity ring down technique where an optical cavity is inside a low temperature cryostat. Absorptions below 12,000 cm−1 were observed with a Fourier transform spectrophotometer. The local mode harmonic frequency and anharmonicity were obtained and used with the harmonically coupled anharmonic oscillator (HCAO) model to calculate energy levels and assign the absorption bands to particular transitions. Overtone absorptions (Δυ = 5 and 6) of CH4 and CH2D2 have also been obtained. The integrated absorption was calculated as a function of the density of the gas samples and used to obtain the band strength and the cross- section of the Δυ = 5 and 6 C–H transitions for each molecule. Cross–sections for CH4 agree within 10% with traditional absorption measurements with a multiple pass cell at high pressures. The importance of the new experimental technique is emphasized for laboratory studies of planetary atmospheres.

Transition probabilities of molecular systems in the presence of time dependent electric fields

Abstract Analytical expressions for the transition probabilities of a molecular system interacting with a low intensity time dependent electric field are derived in the present contribution. The molecular system is modeled as a quartic anharmonic oscillator, where the interaction with the electric field is described by the electric-dipole approximation. Using Lie algebraic techniques and typical states of quantum optics, we are able to obtain an approximate analytical expression for the temporal evolution operator in the present model system.

Ab initio basis set study of the CO⋯He van der Waals interaction

Abstract The ab initio potential energy surface for the weakly bound van der Waals CO⋯He has been performed in the framework of the supermolecule approach, using fourth order Moller–Plesset perturbation theory with different basis sets, constructed to give accurate values for the electric moments and polarizabilities, supplemented by bond functions placed at the midpoint along the line joining He with the center of mass of CO. All atom-centered basis sets explored in the present study predict single-minimum near collinear C–O⋯He optimum structures. Near T-shaped optimum structures are predicted when these basis sets are augmented with a set of bond functions located in the middle of the van der Waals bond, in agreement with recent experimental and ab initio potentials.

MBPT study of the CO-H2 van der Waals interaction

Abstract The many-body perturbation theory (MBPT) is employed for the calculation of the intermolecular interaction potential for the linear CO … H 2 dimer in the framework of the supermolecule approach, using the POL1 basis described recently by Sadlej. This basis set, designed to reproduce electric properties of molecules accurately, leads to a correct calculation of the counterpoise-corrected interaction energies, in excellent agreement with results obtained in the larger basis set used in this study for comparison, and with the best theoretical values available to date. The minimum of the MBPT(4) interaction energy curves occurs at 8.14 and 8.03 a 0 , with well depths of 9.16 and 10.66 meV for the POL1 and larger basis set calculations, respectively. In agreement with very recent spectro- scopic results, a vibrationally bonded ground state is also predicted for this linear dimer.

A fluorescent benzothiazole probe with efficient two-photon absorption.

In this work, we report the two-photon absorption of 2-[4-(dimethylamino)phenyl]-1,3-benzothiazole-6-carbonitrile (DBC) in DMSO solution pumping at 779 nm with a 10 ns pulse laser-Nd:YAG system. The obtained two-photon absorption cross-section in DBC (407 ± 18 GM) is considerably high. Because DBC is a novel compound and have high values of fluorescence quantum yield, this result is expected to have an impact in biomolecules detection, diagnosis and treatment of cancer. Similar structures have previously been reported to show remarkable antitumour effects.

Evaluation of photosensitizers singlet oxygen production for photodynamic therapy applications using time resolved thermal lens

We report on the optical characterization and measurement of oxygen singlet quantum yield of Chlorophyll and Chlorin e6 in water-ethanol mixtures by direct observation of thermal relaxation using time resolved thermal lens method. The analysis of the time-resolved curve allows the determination of the quantum yield of singlet oxygen formation. The quantum yield is deduced from the relative magnitudes of the fast and slow components.

Four-wave mixing spectroscopy of two-level system with intramolecular coupling: the effect of relaxation times

A study has been made of the effect of relaxation times on the four-wave mixing (FWM) signal response in frequency space for a two-level system where intramolecular coupling is explicitly taken into account within a vibronic model. The model is a generalization of the conventional two-level approach in that it includes a simplified description of the molecular structure and the explicit consideration of permanent dipole moments. Significant changes in both the intensity and shape of the peaks of the FWM spectrum are observed, due mainly to changes in the ratio between the longitudinal and transversal relaxation times, T 1/T 2.

Modification in the Relaxation Times and Strength Constant of potential curves in Four-Wave Mixing

In this work we have studied the changes in the Four-Wave Mixing (FWM) signal with the changes in the ratio between the longitudinal and transversal relation times T1/T2. Moreover, we have studied too the modifications in the FWM signal with the changes in the strength constant of the crossed harmonic potential curves that describe the two- levels system employed to this study. We have included the permanent dipolar moments of the states in the uncoupled basis. The rotating wave approximation is neglected to observe the process out of the resonance region. We observed changes in the shape, intensity and position in the resonances of the FWM signal spectra, with the changes in the ratio T1T2 and the strength constant (delta) .

Intramolecular coupling effects on the four-wave mixing signal

In this work we have studied the effect of the intramolecular coupling on the spectral properties of an ensemble of two-level systems carrying homogeneously distributed resonance frequencies, considering permanent dipole moments non zero for a Malachite Green solution.