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
AA. This spectrum shows marked similarities to the standard absorption spectrum of
Cs2. The implications for the molecular potentials of
Cs2 will be discussed.
Abstract Photoionization of a weakly bound van-der-Waals dimer, composed of two atomic speciesAandB, is studied theoretically. AtomAcan be ionized either directly or via an indirect two-center channel, where atomBis first resonantly photoexcited and, afterwards, transfers the excitation energy via long-range electron–electron correlations radiationlessly to atomA, causing its ionization. By taking the vibrational nuclear motion of the dimer during the process into account, we analyze the contributions to the photoionization cross section from bound and dissociative molecular states in the final A+ –Bsystem. For the specific example of a LiHe dimer we show (a) that substantial contributions to both ionization mechanisms result from dissociative Li ++ He states and (b) that the two-center pathway strongly dominates over the direct photoionization channel for photon energies close to one of the molecular LiHe resonances.