We present a study of the multiphoton ionization spectrum of chlorine in the region of 2thinsp;1Pgr;ularr;Xthinsp;1Sgr;+g(1,0ndash;0) threehyphen;photon resonances. Spectra at various pressures were obtained with different polarizations and counterpropagating beam experiments were carried out to restore the peaks quenched by third harmonic interference effects. Chlorine atoms, caused by photodissociation, produce prominent lines in the spectrum and are also responsible for third harmonic generation (THG) which in turn excites some spinhyphen;forbidden transitions by onehyphen;photon absorption. We discuss the change of polarization behavior in the presence of THG and the resultant effect on the symmetry assignments of the excited states. We also discuss third harmonic destructive interference effects in molecular systems and show that total suppression of threehyphen;photon transition to onehyphen;photon allowed states, common in atoms, will not usually occur in molecules although in general changes in polarization behavior should be observed at higher pressures. This conclusion is demonstrated in the chlorine spectrum.
展开▼
