K. Gasmi

Femtosecond time-resolved electron spectroscopy of the intracluster reaction in Ba⋯FCH3

Abstract Applying femtosecond pump–probe spectroscopy combined with the coincidence detection of photoelectrons and photoions, we have analyzed the energetics of the photoinitiated intracluster reaction in Ba⋯FCH 3 on the femtosecond time scale. The rate-determining process of internal conversion from the initially excited A state of the complex to the next lower electronic A′ state was directly observed within a few 100 fs after the initiation of the reaction by the 130 fs laser pulse at 618 nm. Thus, the theoretical analysis of the reaction which is based on the calculation of the corresponding potential energy surfaces was confirmed.

Wave packet dynamics on the repulsive potential surface of BaFCH3 excited at 745 nm

Abstract We studied the time evolution of the wave packet formed by the excitation of the Ba⋯FCH 3 complex with a 120 fs laser pulse at 745 nm to its electronic A ′ state which is repulsive at the ground state geometry and decays to Ba and CH 3 F fragments. By applying probe pulses with different wavelengths of 400 and 267 nm, respectively, we observed strongly different time dependences of the pump–probe signals for the BaF + and Ba + ions determined by the Franck–Condon windows available in both cases. The experimental results are qualitatively confirmed by theoretical studies based on ab initio calculations of the corresponding potential energy surfaces.

Molecular beam depletion by homogeneous and oscillating electric fields

Abstract As was suggested by a theoretical study made by one of us [An. Fis. 93 (1997) 105] the attenuation of a N 2 O supersonic beam was observed when molecules interact with both a homogeneous electric field and a radiofrequency resonant with the Stark N 2 O(1,±1)→(1,0) transition. The experimental observation of the new phenomenon opens interesting possibilities not only for fundamental research but also for technological applications, as for example the development of new analytical techniques based on such a molecular beam depletion.

Nitric Oxide Beam Intensity Oscillations Induced by the Combined Action of a Static and a Radio Frequency Electric Field

This paper details an experimental and theoretical investigation in which a simplified version of the molecular beam electric resonance technique is employed that requires the use of a C-field only. In the experiment the forward intensity of a NO beam is measured as a function of the frequency of the oscillating electric field over the 900-1460 kHz range. Specifically, the interaction of the NO beam with a radio frequency (rf) field of 1.12 kV/m amplitude and -610 kV/m (2) of gradient at the horizontal plane during 72 micros produces a series of oscillations in the transmitted beam intensity. The theoretical analysis shows how the interaction between a beam of NO molecules and both a static and oscillating rf field produces interferences in the forward beam intensity and how the observed interferences are due to superposition of molecular internal states. Furthermore, the interference model reproduces satisfactorily the observed beam intensity oscillations. The present technique could be useful for the development of new schemes to achieve coherent control of molecular processes using radiowaves.

Isotopic and internal CX3 (X=D,H) rotational motion effects in the Ba⋯FCX3+hν→BaF+CX3 intracluster reactions

Photodepletion and action spectra of the laser-induced Ba...FCD3 fragmentation have been measured over the 16 075-16 380 cm(-1) range. The observed band and peak structures allowed us to estimate the vibrational and rotational structures of the excited complex at the transition state configuration. The relative reaction probability P(R)(E) for the intracluster Ba...FCD3 + h nu --> BaF + CD3 reaction has been determined over the cited energy range. P(R)(E) shows a peak structure with an energy spacing of 8.9 cm(-1) which was attributed to an internal rotation of the CD3 group in the intermediate state. A comparison with previous Ba...FCH3 photofragmentation spectra reveals the dynamical role of the internal CX3 (X = H,D) motion which is manifested by the presence of rotational resonances in the laser-induced intracluster reaction.

Excitation laser fluence effects on the Ba⋯FCH3+hν→BaF+CH3 intracluster reaction

Abstract In this work, results on the Ba ⋯ FCH 3 +hν→ BaF ( Ba ∗ )+ CH 3 ( CH 3 F ) reaction obtained under high laser field conditions are reported. We have found that the two-photodissociation channel yields, i.e. the reactive BaF and non-reactive Ba ∗ products, exhibited opposite behaviour depending upon the laser fluence. Whereas the BaF yield rises as the laser fluence is increased, the Ba ∗ yield decreases over the same laser fluence range. In other words, the product ( Ba ∗ ) /(BaF) branching ratio changes significantly from low to high laser fluence in such a way that the (photoinitiated) Ba⋯FCH3→BaF+CH3 reaction may be controlled by changing the intensity of the excitation laser field.