Predissociation And Collisional Depopulation Of Alkali Molecules In The Excited State

The dissertation is devoted to the analysis and study of three processes in experiment. These are photodissociation process of alkali molecules, population process of the excited states of alkali atoms and alkali molecules populated by predissociation and collision transfer of alkali molecules and two kind of collisional energy transfer process between the excited states of alkali molecules and the excited states of alkali atoms.The results of experiments concerning as follow: 1) Populations of the n2L(nL=7P,6D)states of Cs atoms by photodissociation of Cs2 molecules through the use of the fixed frequency line 441.6nm of a He-Cd laser radiation are produced. Combining ratios of atomic to molecular fluorescence at the Cs density range between 1 and 9×1015cm-3,the ratios of collisional rate coefficient to predissociation rates are estimated to be 3.1×10-17cm3 and 1.2×10-17cm3, respectively. The branching ratios are defined as the ratios of nLJ to nLJ' fluorescence. The ratios of the dissociation rates produced in n2L fine structure states are 0.53 and 0.43,respectively. The cross section for excitation transfer out of the 6D doublet [i.e., Cs (6D)+Cs (6S) →states other than Cs (6D)] is 1.9×10-14cm2. The cross section for the fine-structure-changing collision [i.e., Cs (7P1/2)+Cs (6S) →Cs (7P3/2)+Cs (6S)] is 3.5×10-14 cm2. The calculated result for the geometrical cross-section of excited Cs 72P state shows that the magnitudes of σ12 and σ21 can be described relatively well by σgeom. 2) The B1Πu electronic state of Na2 is excited by the 441.6nm He-Cd laser line. The Na atomic transitions and the A1Σ+u→X 1Σ+g band of Na2 have been recorded. From the intensities and spectra of the Na and Na2 fluorescence several collisional processes in the excited sodium atom-dimmer system have been identified. The Na atomic lines are the result of collisional energy transfer from the Na2(B1Πu) to the Na(3P).Predissociation process may also contribute to atomic fluorescence. The A1Σ+u→X 1Σ+g band is interpreted through a populating mechanism involving collisional transfer from the B1Πu to the 21Σ+g followed by radiative transfer to the A1Σ+u state. From the decay constants and fluorescence intensities, the rate coefficient at 360℃ for collisional energy transfer from Na2(B1Πu) to Na2(21Σ+g) is 5.7×10-10cm3S-1.The predissociation rate of the B1Πu is 2.7×106S-1. 3) Depopulation mechanisms of a high-lying state of Na2 are studied using the two-photon absorption technique. The temperatures of the Na vapor were in the range from 623K to 693K. The predissociation and collisional transfer are monitored by the atom sodium emission on the nL→3P transition. Rations of various predissociation rates and collisional transfer rate coefficients are obtained. The contributions to the rate coefficients from other processes are discussed.The whole thesis consists of four chapters. Chapter one is a brief overview of predissociation and collision transfer effect on the excited states of alkali atoms and alkali molecules. Modern laser techniques improved the sensitivity and resolution of spectrum detection, and laser spectroscopy method now plays an important role in the molecular spectroscopy studies. This Chapter has explained mainly the meaning, the background, current situation and main research work in which collision and spectrum of atom molecule studied. Chapter two interpreted all kinds of process, several principles and two methods. Process included radiation, transition, dissociation, collision, and so on. This Chapter also interpreted Franck-Condon principle, setting-up of the speed equation, laser-induced fluorescence and two-photon absorption technique. By these illustrations, we can acquire a basic sight on predissociation and collision depopulation mechanisms. Chapter three we designed and set up a highly sensitive and high-resolution experiment facilities. This Chapter introduced experiment apparatus, the system preparing sample, the detected system, experiment course and steps. Chapter f...