Photodissociation Dynamics Of D₂ And HD Molecule Near Their Thresholds

Photodissociation is the process in which a molecule absorbs photons and dissociates into fragments.The spectrum of hydrogen molecule,especially its energy level structures and dissociation dynamics in highly excited states,has become a benchmark for calculations and experimental techniques.With the developing of laser technology and detection methods,researchers have carried out extensive studies on the angular distribution of dissociation products,angular-resolved spectrum,cross-sections of collision reactions.In this dissertation,a tunable extreme ultraviolet laser(XUV)is used as the pump source to further explore the new phenomena of D2 and HD molecules in photodissociation,and some important research results have been obtained.For the dissociation channel in D2 and HD,we studied the branching ratio 2s/(2s+2p)from the dissociation threshold to 3000 cm-1 above it.The experimental results show that the branching ratio of the dissociated products will oscillate periodically.We use the one-dimensional potential well model to explain the experimental phenomena.The direct dissociation process can be equivalent to the scattering of wave function in the potential well,and the oscillation of the branching ratios results from the mutual interference of the scattered wave functions.Experimentally,the rotation-resolved angular distributions and branching ratios of the dissociation products were detected by tuning the XUV energy along the R-branch transitions of D2 molecular in the 3p?D1?u+(v=4)state.The experiment shows that the angular distributions and branching ratios around the predissociation transition are asymmetric,and the minimum positions deviate from the resonance frequencies of the predissociation transitions.The simultaneous shape resonance and Feshbach resonance of D2 molecular in 2p?C1?u±(v=19)state are studied by the spin-orbital-resolved Rydberg ionization spectra and velocity map imaging.The experiment shows that the spin-orbital branching ratios have reached the limit of the diabatic model,proving the existence of spin-orbital interaction at the dissociation limit.Since the shape resonance and Feshbach resonance are excited simultaneously,the velocity map imaging shows that the angular distributions of products from the two resonances are consistent.Using the Rydberg tagging technique,the angular-resolved Fano profile for the P(2)transition in the 3p?D1?u+(v=4)state of D2 has been measured.The result shows that the Fano profiles have different Fano parameters for the fragments recoiling at the parallel or perpendicular direction relative to the polarization direction of XUV laser.This indicates that the optical transitions to the resonant state and predissociation state have different symmetries.For the HD molecule,the relative populations of the predissociation products H(2s)+D(1s),H(2p)+D(1s),D(2s)+H(1s)and D(2p)+H(1s)were measured.Among them,the proportion of H(2p)/D(2p)and H(2s)/D(2s)is not 1,indicating that there is a strong g-u states mixing at the dissociation limit,leading to the g-u symmetry breaking.In addition,the parameters of the Fano profiles and the angular distributions of the products are not affected by the isotope effect and g-u symmetry breaking.