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The model Hamiltonian approach of Köppel et al. [Adv. Chem. Phys. 57, 59 (1984)] is used to analyze the electronic spectroscopy of the nitrate radical (NO3). Simulations of negative ion photodetachment of NO3-, the X 2A2′←B 2E′ dispersed fluorescence spectrum of NO3, and the B 2E′←X 2A2′ absorption spectrum are all in qualitative agreement with experiment, indicating that the model Hamiltonian contains most or all of the essential physics that govern the strongly coupled X 2A2′ and B 2E′ electronic states of the radical. All 14 bands seen in the dispersed fluorescence spectrum below 2600 cm-1 are assigned based on the simulations, filling in a few gaps left by previous work, and 7 additional bands below 4000 cm-1 are tentatively assigned. The assignment is predicated on the assumption that the ν3 level of NO3 is near 1000 cm-1 rather than 1492 cm-1 as is presently believed. Support for this reassignment (which associates the 1492 cm-1 band with the ν1+ν4 level) comes from both the model Hamiltonian spectrum and a Fourier-transform infrared feature at 2585 cm-1 that is consistent with the large and positive cross anharmonicity between ν1 and ν4 needed for the alternative 1492 cm-1 assignment. An apparent systematic deficiency exists in the treatment of the model Hamiltonian for levels involving ν4. A discussion of the correlation between energy levels in the rigid D3h and C2v limits is illustrative, and provides insight into just how hard it is to treat the degenerate bending coordinate (q4) of NO3 accurately. [ABSTRACT FROM AUTHOR]

The UV/visible spectra of a series of indigo derivatives have been evaluated by using ab initio methods. The combination of the Polarizable continuum model for estimating bulk solvent effects with the TD-B3LYP/6-311+G(2d,p)//B3LYP/6-311G(d,p) level of approximation, leads to an accurate description of the wavelength of maximum absorption of indigoïds compounds. Using this procedure, we have assessed the effects of both the surroundings (solvent and solid state) and the substitution pattern. For the latter, we obtained a mean absolute deviation of only 7 nm (0.02 eV) compared to experiment, for a set of 86 molecules/solvents. [ABSTRACT FROM AUTHOR]

We have investigated theoretically the interband excitonic absorption spectra and the coupling behaviors of coupled symmetric triple Zn1-xCdxSe/ZnSe quantum wells with diluted Mn doping in the central well under external magnetic field. The results show that the magnetic field can effectively adjust the energy levels and the optical properties of the coupled multiple quantum wells (CMQWs). The coupling behaviors of the CMQWs are very sensitive to the central well depth. The effect of the magnetic-field-introduced parabolic-confined potential on the main features of the absorption spectra can be neglected at moderate magnetic-field densities. [ABSTRACT FROM AUTHOR]

A general formulation of nonperturbative quantum dynamics of solutes in a condensed phase is proposed to calculate linear and nonlinear vibrational line shapes. In the weak solute-solvent interaction limit, the temporal absorption profile can be approximately factorized into the population relaxation profile from the off-diagonal coupling and the pure-dephasing profile from the diagonal coupling. The strength of dissipation and the anharmonicity-induced dephasing rate are derived in Appendix A. The vibrational energy relaxation (VER) rate is negligible for slow solvent fluctuations, yet it does not justify the Markovian treatment of off-diagonal contributions to vibrational line shapes. Non-Markovian VER effects are manifested as asymmetric envelops in the temporal absorption profile, or equivalently as side bands in the frequency domain absorption spectrum. The side bands are solvent-induced multiple-photon effects which are absent in the Markovian VER treatment. Exact path integral calculations yield non-Lorentzian central peaks in absorption spectrum resulting from couplings between population relaxations of different vibrational states. These predictions cannot be reproduced by the perturbative or the Markovian approximations. For anharmonic potentials, the absorption spectrum shows asymmetric central peaks and the asymmetry increases with anharmonicity. At large anharmonicities, all the approximation schemes break down and a full nonperturbative path integral calculation that explicitly accounts for the exact VER effects is needed. A numerical analysis of the O–H stretch of HOD in D2O solvent reveals that the non-Markovian VER effects generate a small recurrence of the echo peak shift around 200 fs, which cannot be reproduced with a Markovian VER rate. In general, the nonperturbative and non-Markovian VER contributions have a stronger effect on nonlinear vibrational line shapes than on linear absorption.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Unsaturated absorption coefficients in pure carbon dioxide at pressures of 1 and 100 Torr and in CO-N and CO-He binary mixtures at a pressure of 100 Torr have been measured in the temperature range of 296-700 K using a frequency-stabilized tunable CO laser. The collisional self-broadening coefficient, the relative coefficients of collisional broadening caused by N and He buffer gases, and their temperature dependences have been determined for the R22 absorption line of the 100-001 transition in CO molecules. [ABSTRACT FROM AUTHOR]

Optical spectroscopy and nanosecond flash photolysis (Nd:YAG laser, 355 nm, pulse duration 5 ns, mean energy 5 mJ/pulse) were used to study the photochemistry of Fe III(C 2O 4) 33−complex in aqueous solutions. The main photochemical process was found to be intramolecular electron transfer from the ligand to Fe(III) ion with formation of a primary radical complex [(C 2O 4) 2Fe II(C 2O 4•)] 3−. The yield of radical species (i.e., CO 2• −and C 2O 4• −) was found to be less than 6% of Fe III(C 2O 4) 33−disappeared after flash. [(C 2O 4) 2Fe II(C 2O 4•)] 3−dissociates reversibly into oxalate ion and a secondary radical complex, [(C 2O 4)Fe II(C 2O 4•)] −. The latter reacts with the initial complex and dissociates to Fe II(C 2O 4) and oxalate radical. In this framework, the absorption spectra and rate constants of the reactions of all intermediates were determined. [ABSTRACT FROM AUTHOR]

In the present work, results of investigations into the transient absorption of some organic compounds by the method of pulsed flash photolysis are given. Experimental investigations were carried out using an original setup of pulsed flash photolysis with an exciting pulse of XeCl-laser radiation of nanosecond duration and sensing by broadband laser-transient fluorescent radiation of a mixture of organic fluorophors called “white light” excited by the same source in the wavelength range 330–750 nm. The setup registers the short-living (singlet-singlet) and long-living (triplet-triplet) absorptions. The transient absorption spectra of already investigated para-terphenyl, naphthalene, and 1-phenyl-2(2-naphthyl)-ethylene molecules are presented; the spectra of the transient absorption and its nature are in good agreement with the experimental and calculated data published in the literature. We first investigated the transient absorption of LOC1 (S1-Sn at 580 nm and T1-Tn at 500 nm) and phenalemine 512 (S1-Sn at 395 nm). It is demonstrated that the experimentally observed induced absorption of phenalemine 512 and PD 789 is the S1-Sn absorption, which is in good agreement with the results of quantum-chemical calculations. [ABSTRACT FROM AUTHOR]