Multiphoton Ionization of K2 in the Wavelength Range 600–670 nm

The relative production rates of K + and K 2 + ions through the multiphoton ionization of K 2 are measured in the wavelength range 600–670 nm. These rates for K 2 + ions have a threshold at about 600 nm and a broad peak at about 620 nm. These for K + ions have the threshold at about 612 nm and the position of the peak is roughly equal to that of K 2 + ion. The effective order of nonlinearity k , which is the minimum number of photons necessary to ionize the K 2 molecule, is measured as a function of the wavelength. k for K + ions is about 3 in 613–650 nm, except for that at 634 nm, at which k is about 2.3. On the other hand, k for K 2 + is about 2 in the wavelength range shorter than 611 nm and two values of k in 632–637 nm are about 1.6. Beyond 637 nm, k increases with an increase of wavelength and reaches about 2.6 at 650 nm. From these results, the production processes of K + and K 2 + ions are discussed.