Abstract

Ionic molecules such as LiF are ideal candidates for above-threshold photodissociation, the analog of above-threshold ionization. These molecules dissociate into two channels, an ionic channel Li⁺F⁻ and a covalent channel, i.e., neutral LiF atoms. Both channels are coupled by nonadiabatic interactions. Coupled-equation calculations of nonresonant multiphoton absorption by IR photons (ω_LiF = 800 cm⁻¹, ω_photon = 5000, ω = 2000, ω = 1064 cm⁻¹) demonstrate the analogy with above-threshold ionization, i.e., the ionic fragments continue to absorb photons well above the dissociation limit in spite of nonadiabatic branching into the neutral channel. It is estimated that these effects should be observable at intensities higher than 10¹² W/cm² owing to the large dipole moment of the ionic fragments on dissociation. Furthermore, at these high intensities the ionic products predominate over the neutral products by 1 order of magnitude.

© 1990 Optical Society of America

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