Imaging the state-specific vibrational predissociation of hydrogen bonded complexes

Unrestricted In this dissertation the dynamics of the vibrational predissociation of three hydrogen bonded dimers, acetylene-ammonia, acetylene-HCl and acetylene-DCl, are presented and discussed. High spectral and energy resolution were achieved using velocity map imaging in conjunction with resonance enhanced multiphoton ionization. Pair-correlated fragment rotational state distributions were obtained and dissociation energies were determined.; The vibrational predissociation of the acetylene-ammonia dimer was studied following excitation of the asymmetric CH stretch. Dissociation fragments were produced with vibrational excitation distributed in a very specific way. Ammonia fragments were always generated vibrationally excited with one or two quanta of the umbrella mode, while bending levels were excited in acetylene. A dissociation energy of 900 ± 10 cm-1 was determined. The rotational state populations of both the ammonia and acetylene fragments were reproduced well by McCaffery using the angular momentum model.; The acetylene-HCl dimer was studied following excitation of both the asymmetric CH stretch and the HCl stretch. Different vibrational predissociation mechanisms take place following asymmetric CH and HCl stretch excitations. The couplings between the intermolecular and intramolecular modes that govern vibrational to vibrational and vibrational to translational energy transfer are sensitive to the location of the initial vibrational mode excited in the dimer. Asymmetric CH stretch excitation leads to CC stretch excitation in acetylene fragments and rotational excitation in HCl fragments. HCl stretch excitation resulted in rotationally excited HCl fragments and acetylene fragments excited in combinations of the bends. A dissociation energy of 700 ± 10 cm-1 was determined. The rotational state populations of both the acetylene and HCl fragments following HCl stretch excitation were examined by McCaffery using the angular momentum model.; The acetylene-DCl dimer was studied following excitation of the asymmetric CH stretch. The results are similar to those obtained for the acetylene-HCl dimer. A dissociation energy of 755 ± 10 cm-1 was determined. The difference in the dissociation energies of the acetylene HCl and acetylene-DCl dimers was attributed to differences in vibrational zero point energies. No vibrationally excited DCl fragments were detected, although this excitation is energetically accessible.