Molecular quantum beats

Bitto, H., and Huber, J. R. (1992), Molecular Quantum Beats. High-Resolution Spectroscopy in the Time Domain, Acc. Chem. Res. 25, 65. 

Many other molecules, such as SO2 [880], NO2 [881], or CS2 [882], have been investigated. A fine example of the capabilities of molecular quantum-beat spectroscopy is the determination of the magnitude and orientation of excited-state electric dipole moments in the vibrationless Si state of planar propynal [883]. 

H. Bitto, J.R. Huber, Molecular quantum beat spectroscopy. Opt. Common. 80,184 (1990) R.T. Carter, R. Huber, Quantum beat spectroscopy in chemistry. Chem. Soc. Rev. 29, 305 (2000)... 

H. Bitto, J.R. Huber Molecular quantum beat spectroscopy. Opt. Commun. 80, 184 (1990)... 

J. Jortner and R.S. Berry, Radiationless Transitions and Molecular Quantum Beats , J. Chem. Phys. 48, 2757 (1968). 

Jortner, J. and Berry, R.S. (1968) Radiationless transitions and molecular quantum beats./. Chem. Phys., 48, 275. 

Leonhardt R, Holzapfel W, Zinth W and Kaiser W 1987 Terahertz quantum beats in molecular liquids Chem. Phys. Lett. 133 373-7... 

The nature of the radiative decay in the resonance and in the statistical limits was considered by Berry and Jortner,7 who examined the interference effects in the radiative decay of coherently excited states. Quantum beat signals can be observed and used to analyze close-lying molecular... 

It should be noted that the laser pump pulses create sets of intermolecular rovibrational coherence. For example, quantum beats appear in time profile of the CARS spectrum from a molecular mixture. - The beat frequency created is equal to the difference between frequencies of vibrational modes of molecules in the mixture. When many sets of inteimolecular... 

The development of the picosecond-jet technique is presented. The applications of the technique to the studies of coherence (quantum beats), photodissociation, isomerization and partial solvation of molecules in supersonic-jet beams are detailed with emphasis on the role of intramolecular energy redistribution. Experimental evidence for intramolecular threshold effect for rates as a function of excess molecular energy is given and explained using simple theory for the redistribution of energy among certain modes. Comparison with R.R.K.M. calculation is also made to assess the nature of the statistical behaviour of the energy redistribution. 

The time-dependent oscillations in absorption or other observables can be thought of as quantum beats resulting from coherent excitation of several vibronic levels contained within the bandwidth of the ultrashort excitation pulse. In a formal sense, the experiment is the same as other quantum beat experiments carried out on femtosecond or longer time scales. However, in most such experiments different molecular vibrational degrees of freedom that... 

The second major section (Section III), comprising the bulk of the chapter, pertains to the studies of IVR from this laboratory, studies utilizing either time- and frequency-resolved fluorescence or picosecond pump-probe methods. Specifically, the interest is to review (1) the theoretical picture of IVR as a quantum coherence effect that can be manifest in time-resolved fluorescence as quantum beat modulated decays, (2) the principal picosecond-beam experimental results on IVR and how they fit (or do not fit) the theoretical picture, (3) conclusions that emerge from the experimental results pertaining to the characteristics of IVR (e.g., time scales, coupling matrix elements, coupling selectivity), in a number of systems, and (4) experimental and theoretical work on the influence of molecular rotations in time-resolved studies of IVR. Finally, in Section IV we provide some concluding remarks. 

Figure 9.5 The phase of a vibrational quantum beat depends on whether the bright state for the excitation step is bright or dark in the fluorescence detection step, A molecular beam of anthracene, rotationally cooled to 3K, is excited by a 15 picosecond pulse at 1420 cm-1 above the Si <— So 0q origin band. Fluorescence is detected in a selected wavelength region through...

The phase shifts of quantum beats have been studied in other alkanes as well [30], As expected, in linear alkanes the rate constants of hole trapping by acceptors, determined from the shifts, were close to the diffusion-controlled ones. In cyclic alkanes (cyclohexane, czs-decalin, and trans-decalin), the hole mobility is known to considerably exceed the mobility of molecular ions [31]. In these solvents the observed phase shifts had an intermediate value between that expected for the highly mobile holes and that assumed for molecular ions. Both types of ions are likely to take part in the formation of diphenylsulphide radical cation in cyclic alkanes. 

Molecular fragment responsible for hfi Atom A,G OD ESR A,G Quantum beats... 

Either two or more molecular levels of a molecule are excited coherently by a spectrally broad, short laser pulse (level-crossing and quantum-beat spectroscopy) or a whole ensemble of many atoms or molecules is coherently excited simultaneously into identical levels (photon-echo spectroscopy). This coherent excitation alters the spatial distribution or the time dependence of the total, emitted, or absorbed radiation amplitude, when compared with incoherent excitation. Whereas methods of incoherent spectroscopy measure only the total intensity, which is proportional to the population density and therefore to the square ir of the wave function iff, the coherent techniques, on the other hand, yield additional information on the amplitudes and phases of ir. 

Quantum-beat spectroscopy represents not only a beautiful demonstration of the fundamental principles of quantum mechanics, but this Doppler-free technique has also gained increasing importance in atomic and molecular spectroscopy. Whereas commonly used spectroscopy in the frequency domain yields information on the stationary states A ) of atoms and molecules, which are eigenstates of the total Hamiltonian... 

Because quantum-beat spectroscopy offers Doppler-free spectral resolution, it has gained increasing importance in molecular physics for measurements of Zee-man and Stark splittings or of hyperfine structures and perturbations in excited molecules. The time-resolved measured signals yield not only information on the dynamics and the phase development in excited states but allow the determination of magnetic and electric dipole moments and of Lande g-factors. 

G. Herzberg, Molecular Spectra and Molecular Structure (van Nostrand, New York, 1950) N. Ochi, H. Watanabe, S. Tsuchiya, RotationaUy resolved laser-induced fluorescence and Zeeman quantum beat spectroscopy of the state of jet-cooled CS2. Chem. Phys. 113,... 

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