The double photoionization of HCl: An ion-electron coincidence study

The double photoionization of HCl molecules by synchrotron radiation has been studied in the energy range between 30 and 50 eV. The HCl21 and Cl21 product ions have been detected by a photoelectron–photoion-coincidence technique, while the H11Cl1 formation, which follows the double ionization of HCl, has been studied by photoelectron–photoion–photoion coincidence. The photon energy threshold for the production of HCl21 ions has been found to be 35.460.6 eV, while for the dissociative channel leading to H11Cl1, it has been measured a threshold at 36.460.6 eV and a change in the slope of the cross-section energy dependence at 38.760.7 eV. The production of H1Cl21 occurs with a threshold photon energy of 42.861.1 eV. These results appear to be in a good agreement with previous data by different experimental techniques and recent theoretical calculations performed by our laboratory

The Geometric Phase Controls Ultracold Chemistry

The geometric phase is shown to control the outcome of an ultracold chemical reaction. The control is a direct consequence of the sign change on the interference term between two scattering pathways (direct and looping), which contribute to the reactive collision process in the presence of a conical intersection (point of degeneracy between two Born–Oppenheimer electronic potential energy surfaces). The unique properties of the ultracold energy regime lead to an effective quantization of the scattering phase shift enabling maximum constructive or destructive interference between the two pathways. By taking the O+OH→H+O2 reaction as an illustrative example, it is shown that inclusion of the geometric phase modifies ultracold reaction rates by nearly two orders of magnitude. Interesting experimental control possibilities include the application of external electric and magnetic fields that might be used to exploit the geometric phase effect reported here and experimentally switch on or off the reactivity