Light fluorescence, collision-induced

In spite of the fact that in alkali vapors, which contain about 1 % diatomic alkali-molecules at a total vapor-pressure of 10 torr, the atoms cannot absorb laser lines (because there is no proper resonance transition), atomic fluorescence lines have been observed 04) upon irradiating the vapor cell with laser light. The atomic excited states can be produced either by collision-induced dissociation of excited molecules or by photodissociation from excited molecular states by a second photon. The latter process is not improbable, because of the large light intensities in the exciting laser beam. These questions will hopefully be solved by the investigations currently being performed in our laboratory. 

J. I. Gersten. Collision-induced fluorescent light scattering in atomic gases. Phys. Rev. Lett., 37 73-76 (1973). 

The collisional fluorescence quenching and phosphorescence induction processes have been later observed for a large number of small and medium-size molecules. The interpretation of these results was however rather confusing collision-induced intersystem crossing considered as a transition from the pure singlet to the pure triplet state is in apparent contradiction with the Wigner rule of spin conservation, at least in the case of light collision partners that cannot affect the intramolecular spin-orbit interaction. 

According to (8.11) the optoacoustic signal decreases with increasing quantum efficiency because the fluorescence carries energy away without heating the gas, as long as the fluorescence light is not absorbed within the cell. Since the quantum efficiency is determined by the ratio of spontaneous to collision-induced deactivation of the excited level, it decreases with in-... 

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