Knowledge Bank

A new method for studying dissociative molecular states, complementary to standard spectroscopy techniques, is discussed and its application to the specific case of $Cs2$ is reported. Previous multi-photon ionization $experiments1,2$ revealed the existence of hybrid absorption resonance, in which one photon causes a molecular transition to a dissociative state and a second photon is absorbed by one of the resulting dissociation fragments. The method of dissociation excitation spectroscopy uses two synchronized pulsed lasers to sequentially excite a dissociative molecular state and then detect the dissociation fragments through atomic excitation followed by collisional ionization. By scanning the wavelength of the laser probing the molecule it is possible to obtain a spectrum giving the relative probability that a specific dissociation product will be formed after photo-absorption in the molecule. The dissociation excitation spectrum, including the fine-structure branching ratio, has been obtained for the case [ Cs_{2} + \gamma \rightarrow Cs_{2}^{*} \rightarrow Cs(6^{2}S_{1/2}) + Cs(5^{2}D_{3/2,5/2}) ] over the wavelength region 4575-6050 $\backslash AA$. This spectrum shows marked similarities to the standard absorption spectrum of $Cs2$. The implications for the molecular potentials of $Cs2$ will be discussed.