The angular distribution of electrons ejected from He with about the projectile velocity in coincidence with the capture of the other electron by the projectile in 1-MeV proton-He collisions has been measured. The signature of the proton-electron-electron scattering leading to transfer ionization has been observed for the first time as a peak at about 90° in the angular distribution of the ejected electrons. The effect is in qualitative agreement with theoretical predictions. PACS numbers: 34.50.Fa, Considerable experimental and theoretical effort has been devoted recently to study the intriguing details of atomic collision processes involving the correlated motion of two active electrons. One of the conceptually simplest of these processes is electron capture from He by a fast proton through projectile-electron-electron ip-e-e) scattering. In this process the captured electron first collides with the proton and then scatters into a bound state of the projectile through a second collision with the other target electron, which is ionized due to this scattering. The simultaneous capture and ionization of two target electrons is called transfer ionization (TI) and can occur also through two independent interactions between the projectile and two target electrons. The p-e-e scattering mechanism leading to TI is very similar to the process of electron capture through nuclear double scattering. In that process, first discussed by Thomas* in classical terms, the second scattering of the captured electron occurs on the target nucleus. In the quantummechanical descriptions^'^ these double-scattering processes are represented by the second-order terms in the Born expansion. At very high collision velocities, where capture cannot be facilitated by the high-momentum components of the bound states, these double-scattering processes are the dominant mechanisms of electron capture.The experimental signature of the nuclear doublescattering mechanism is a sharp peak at 0.47 mrad in the angular differential scattering cross section of the charge-changed projectiles, reflecting the fixed kinematics of the first collision of the projectile with the target electron. This signature has been found"* in p-He, and more clearly in p-H collisions.^ Similarly, the p-e-e scattering should result in a peak at 0.55 mrad in the angular differential scattering cross section of chargechanged projectiles, which produce He^"^. Recently Horsdal, Jensen, and Nielson^ found a peak at around 0.55 mrad in the ratio of the differential scattering cross sections of charge-changed 0.3-0.7-MeV protons producing He^"^ and He"'", respectively. This result could, however, be described^ as simultaneous capture and ionization of independent electrons (i.e., without including the electron-electron interaction in the scattering ampli-tude).Briggs and Taulbjerg^ suggested that a signature of the /7-e-^-scattering-mediated capture in p-He collisions would be a peak at Ve = Vp (electron velocity equals the projectile velocity) in the energy spectrum of electrons ejec...

No abstract

No abstract

can note that none of the previous technologies were capable of Lifetimes of 28 different rotational levels of the PH' A 2 A state (v'= 0, 1) have been measured using the High Frequency Deflection technique. Rotational levels above the dissociation limit of the ground state showed influences of predissociations. CASSCF calculations of the electronic transition moment of the A Z A -X'n transition made possible the determination of the lifetimes toward predissociation. CASSCF + CI calculations of the A'A, X'n, 'E-, and TI state potential energy curves were performed. These curves were combined with experimental Rydberg-Klein-Dunham potential energy curves in a scaling procedure in order to obtain accurate potential energy curves which were used in a model calculation of the predissociation rates. These model calculations showed that a second order interaction between the A 2 A state and the 'E-state via an excited state is the most plausible mechanism for the observed predissociation.

EARLINET, the European Aerosol Research Lidar Network, offers a unique opportunity for the validation and full exploitation of the CALIPSO mission because of its geographic coverage and the deployment of advanced Raman aerosol lidars. EARLINET provides long-term, quality-assured aerosol data, which allows us to investigate a large variety of different aerosol situations with respect to layering, aerosol type, mixing state, and properties both in the free troposphere and the local planetary boundary layer. EARLINET started correlative measurements for CALIPSO since 14 June 2006, at the beginning of the operativity of CALIOP. A strategy for correlative measurements has been defined on the base of the analysis of the ground track data provided by NASA. Based on the experience of the first 18 months of correlative observations, the strategy of correlative measurements has been consolidated in the frame of a dedicated ESA study aiming at a long-term aerosol and cloud data base from ground-based and satellite-borne lidars. Within this study, correlative measurements have been intensified especially taking into account the geographical distribution of participating stations. EARLINET correlative measurements are still in progress. After about 3 years of correlative observations, more than 6500 hours of correlative measurements have been performed and about 3100 correlative files are available for comparisons. A number of modelling tools is used for the aerosol type and source identification in addition to the information derived from the multi-wavelength lidar observations. The first results in terms of comparisons between EARLINET and available CALIPSO products (both level 1 and level 2 data) are presented. Comparison EARLINET -CALIPSO (lev1) Comparison EARLINET -CALIPSO (lev1)Reference -Wandinger, U., Pappalardo G., Hiebsch A., Mattis I., Mona L., and Madonna F. (2009), Long-term aerosol and cloud database from correlative CALIPSO and EARLINET observations, this workshop.-Mona, L. , Pappalardo G. , Amodeo A., D'Amico G., Madonna F., Boselli A., Giunta A., Russo F., and Cuomo V. Comparison in terms of CALIPSO Level 1 product is needed for identifying any potential problem and bias contained in the calibrated CALIPSO lidar signals (lev1). Only after a check of the unprocessed CALIPSO data, the comparison in terms of Level 2 products will allow to check and improve CALIPSO retrieval algorithms and assumptions. From simultaneous and independent measurements of aerosol backscatter and extinction profiles measured by EARLINET, it is possible to calculate without any assumptions the CALIPSO-like attenuated backscatter (CLAB) profile at 532 nm, to be compared to CALIPSO Level 1 data [Mona et al., 2009]. Number of occurrences (Calipso-EARLINET)/EARLINET [%]Distribution of the mean relative differences between CALIPSO Level 1 and corresponding EARLINET attenuated backscatter measurements.The calculation has been performed using data provided by the 3+2 stations of Leipzig, Napoli, Potenza, Madrid and Barcelona.Good agreement ...