Flame opto-galvanic spectroscopy

Opto-galvanic spectroscopy detects the absorption spectra of atoms (6) and some molecules (7) in a flame by measuring current changes induced by optical irradiation at a wavelength corresponding to an electronic transition. Two steps are involved ... 

In the previous section we described how optical resonance could be detected by direct observation of electrical phenomena. From this point of view we described a special type of opto-galvanic spectroscopy. When electrical detection of optical resonance in connection with measurements on electrical discharges or flames is performed the term Laser-Enhanced Ionization (LEI) spectroscopy is frequently used. In Fig.9.9 opto-galvanic spectroscopy (LEI) on a gas discharge is illustrated. The laser beam is directed into the discharge and when it is tuned to an optical transition the discharge current is changed, since the probability of collisional ionization is different for... 

Opto-galvanic spectroscopy of flames has important analytical applications. If an atomic absorption flame (Sect.6.5.3) is irradiated by a tunable laser a change in the current between two electrodes, placed in the outer parts of the flame, can be detected. A typical arrangement is shown in Fig. 9.10. A sensitivity exceeding that obtainable in atomic absorption spectroscopy (Sect.6.5.2) can be achieved for elements seeded into the flame. Two-step excitation improves both sensitivity and background rejection. The opto-galvanic technique can also be used for studying normal flame constituents such as O, H and OH [9.60]. 

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