State preparation REMPI

The reason for the name population quantum beats is that the signal intensity (fluorescence, REMPI), integrated over all solid angles and polarization states, oscillates in time after the preparation pulse. It appears as if the population prepared in the excited state at t = 0 vanishes and returns periodically (see Fig. 9.5) (Felker and Zewail, 1984). In fact, the population does not oscillate, but the radiative capability of the time-evolving state prepared at t = 0, k(t), does oscillate. 

Plenary 11. W Kiefer et al, e-mail address wolfgang.kiefer mail.imi-wue.de (TR CARS). Ultrafast impulsive preparation of ground state and excited state wavepackets by impulsive CARS with REMPI detection in potassium and iodine duners. 

This chapter deals mainly with (multi)hyphenated techniques comprising wet sample preparation steps (e.g. SFE, SPE) and/or separation techniques (GC, SFC, HPLC, SEC, TLC, CE). Other hyphenated techniques involve thermal-spectroscopic and gas or heat extraction methods (TG, TD, HS, Py, LD, etc.). Also, spectroscopic couplings (e.g. LIBS-LIF) are of interest. Hyphenation of UV spectroscopy and mass spectrometry forms the family of laser mass-spectrometric (LAMS) methods, such as REMPI-ToFMS and MALDI-ToFMS. In REMPI-ToFMS the connecting element between UV spectroscopy and mass spectrometry is laser-induced REMPI ionisation. An intermediate state of the molecule of interest is selectively excited by absorption of a laser photon (the wavelength of a tuneable laser is set in resonance with the transition). The excited molecules are subsequently ionised by absorption of an additional laser photon. Therefore the ionisation selectivity is introduced by the resonance absorption of the first photon, i.e. by UV spectroscopy. However, conventional UV spectra of polyatomic molecules exhibit relatively broad and continuous spectral features, allowing only a medium selectivity. Supersonic jet cooling of the sample molecules (to 5-50 K) reduces the line width of their... 

Use of REMPI via Rydberg state of Nj to prepare 370 vibrationally state-selected N5(A n )... 

On the experimental side, the coupling of crossed molecular beam techniciues with sophisticated detection techniques (Laser Induced Fluorescence, CARS or REMPI spectroscopy, Rydberg tagging photoionisation using synchrotron radiation or U lasers) has improved considerably the detailed study of chemicid reactivity. It is now possible to prepare reactants in a well defined state and to analyze the reaction products at a fixed scattering angle for a. collision at a well defined kinetic energy [1]. 

The preparation of reagents in selected states and the study of the internal-state distribution of the reaction products by LIF or REMPI brings complete information on the state-to-state molecular dynamics [1411],... 

More recently, methods based on laser preparation of reagent ions and laser-based detection of product ions have been accomplished for the thermal energy charge transfer reaction DBr+ + HBr HBr+ + DBr. REMPI was used to prepare DBr+ in specific vibrational and spin-orbit states, and the HBr+ product state was measured by laser-induced fluorescence. The largest rate constants were observed for near-resonant processes in which both the vibrational and the spin-orbit quantum numbers remained unchanged. 

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