FIGURE 11.18 (a) Potential energy diagram and (b) REMPI schemes for the excitation and ionization of

NO (adapted from Pfab, 1995). The------ indicates a virtual state. The dashed arrows show other transitions used to detect NO in the atmosphere by laser-induced fluorescence (see Section A.4.a(l)).

the rotational transitions. (Note, however, as discussed later, interferences may result if NO is generated by photolysis of other species such as N02 in the laser beam.)

Pumping low-lying Rydberg states as the resonant intermediate is generally preferred over excitation of higher valence states because the latter often predisso-ciate, undergo rearrangement, or intersystem cross before the subsequent absorption of photons can form

225.8 225.9 226.0 226.1 226.2 226.3 226.4 226.5 Wavelength (nm)

FIGURE 11.19 Two-color (1 + 1') REMPI spectrum of the NO (X2n, /■' = 0 -> A22 + , r' = 0) band at 300 K (adapted from Pfab, 1995).

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