Separation of Time Scales in the Dynamics of High Molecular Rydberg States

A large volume ͑hundreds of cm 3 ͒ plasma is created by a 193 nm laser ionizing an organic vapor, tetrakis͑dimethyl-amino͒ethylene ͑TMAE͒. The plasma is characterized as high electron density (10 13 -10 12 cm Ϫ3 ) and low electron temperature ͑ϳ0.1 eV͒. To investigate the plasma decay processes, a fast Langmuir probe technique is developed, including detailed considerations of probe structure, probe surface cleaning, shielding, frequency response of the detection system, physical processes in probe measurement, dummy probe corrections as well as noise analysis. The mechanisms for the plasma decay are studied and a delayed ionization process following the laser pulse is found to be important. This mechanism is also supported by optical emission measurements which show that nitrogen enhances the delayed emission from TMAE plasma. A model combining electron-ion recombination and delayed ionization is utilized together with experimental results to order the terms and calculate the relaxation times for delayed ionization. The relaxation times are longer for lower TMAE pressures and lower electron densities.

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Time and frequency resolved spectra of high molecular Rydberg states by dynamical computations

Remacle

Levine

1997

The Journal of Chemical Physics

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The absorption spectrum of bound Rydberg states which can be detected by a delayed, pulsed field ionization is computed. The spectrum, measured for various delay times, provides information on the short and the longer time dynamics of high molecular Rydberg states. A quantitative dynamical theory, based on an effective Hamiltonian formalism is applied, illustrating the role of the Rydberg electron–core coupling and of an external electrical field in the delay-time dependent spectra. The sharpening of the spectra for longer delay times is reproduced by the dynamical computations. It is found that the overall intensity, as a function of the delay time before detection, is well described by a double exponential decay where the short lifetime is primarily a manifestation of the direct autoionization to the continuum, while the long lifetime is due to interseries coupling. Both lifetimes increase with the principal quantum number of the Rydberg states. The notion of trapped “reservoir states” is illustrated by the computational results, with special reference to a kinetic model analysis. The role of the initially optically accessed state(s) and of the depth of detection, in particular with regard to the intensity, is demonstrated. The effect of varying the strength of an external dc field in the time interval prior to the detection is illustrated by the dynamical computations, with respect to both the decay kinetics and the intensity of the spectrum.

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Separation of Time Scales in the Dynamics of High Molecular Rydberg States

Cited by 6 publications

References 65 publications

Delayed Ionization

Delayed Ionization

Diagnostics and analyses of decay process in laser produced tetrakis(dimethyl-amino)ethylene plasma

Time and frequency resolved spectra of high molecular Rydberg states by dynamical computations

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