“…thermore, multiphoton absorption cross sections in many systems remain constant as a function of fluence, implying an absorption cross section that does not significantly vary as a function of level of excitation. 58,59 In such systems, densities of states approach the criterion used for the onset of the quasi-continuum, ca. 100 states/cm"1, near 3000 cm"1, i.e., approximately the v = 3 level of the pumped mode.59 Uranium hexamethoxide has 87 normal modes, many of which are of substantially lower frequency than in the aforementioned hydrocarbon systems.…”