Investigating the Rydberg States and Photodissociation Dynamics of Kr2 using Velocity Map Imaging

Although the krypton dimer, Kr2, is a prototypical weakly bound van der Waals complex in its ground electronic state, the excited states of Kr2 exhibit many and various interactions. Resonance enhanced multiphoton ionization and velocity map imaging provide an avenue to explore the electronic structure and photofragmentation dynamics of Kr2 in the vacuum ultraviolet region. By monitoring photofragmentation product channels and recoil anisotropy distributions, one can gain insights into excited state symmetries and lifetimes, which can aid in interpreting spectroscopy. Here, we study the spectroscopy and photodissociation dynamics of Kr2 in the 91,000 – 94,500 cm-1 region. We record and assign photofragment product channels for 32 vibronic bands corresponding to seven electronic transitions. We also identify two previously unobserved vibronic band systems, which we assign as the Kr2 5p [5/2]3 1g ← X0g+ and 5p [3/2]2 0g+ ← X0g+ transitions. Velocity map images show photofragments arising from predissociation of the neutral Rydberg states and from dissociative photoionization at the n > 2 photon level. We also observe variation in branching ratios between the predissociative and dissociative photoionization channels depending on the lifetime of the intermediate; longer lived states favour higher dissociative photoionization yields and exhibit β6 anisotropy parameters for predissociation product channels, indicating “rotational smearing” of the product angular distributions.