Photoselective resonance ionization of molecules

The earliest experiments on the resonance stepwise photoionization of molecules (H2CO) were conducted by Andreyev et al. (1975) in an ionization chamber without using any mass separation of the photoions produced. The next natural step was the two-stage resonance photoionization of molecules by the scheme of Fig. 10.1, involving mass analysis of the photoions produced (Antonov et al. 1977, 1978). The experimental setup for studying the stepwise photoionization of polyatomic molecules in a mass spectrometer consisted of a static magnetic mass spectrometer and time-synchronized 

The stepwise resonance ionization of molecules differs materially from the resonance photoionization of atoms by, first, the small resonance excitation cross sections of the electronic states in polyatomic molecules, owing to their distribution among many rotational-vibrational levels, and, second, the fact that the absorption bands of many molecules occur in the UV region of the spectrum. For this reason, the soft resonance stepwise photoionization technique has proved unsuitable for the majority of 

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