Abstract

In Laser-Enhanced Ionization spectrometry (LEI) in flames the measured signal consists of the electrons and ionized atoms which follow a laser excitation due to the enhanced thermal ionization rate of an excited state compared with the ground state. The charged particles are collected by applying a voltage across the flame and measuring the corresponding current increase. The authors report the observation of the linear Stark effect in highly excited states of Li in flames when laser-enhanced ionization is utilized. The experiments show good agreement with the theory for the linear Stark effect. The atoms were excited by ultraviolet light from the ground state (2s) to <i>n</i>p states (<i>n</i> = 8-22). Collisional broadening is the dominant broadening mechanism for the lower states while the Stark effect dominates at higher values of <i>n</i> for laboratory electrical field strengths. In the analytical use of LEI for trace element analysis the presence of the Stark effect leads to a reduction of the sensitivity of the method, because it decreases the peak-height of the signal. A new method, which utilizes the Stark effect, is presented for nonintrusive determination of the electrical field distribution in flames.

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