We have measured coincidences between neutral H atoms and Lyman-α photons for collisions between 50-keV protons and noble gases as a function of the projectile scattering angle. The coincidences are dominated by capture to the 2p state of the projectile. While the total cross sections depend strongly on the target, the shape of the angular distribution of the differential cross sections was found to depend only weakly on that parameter. The data indicate that electrons are captured predominantly from the outermost shell of the target atom for the collision systems studied here. We have measured coincidences between neutral H atoms and Lyman-a photons for collisions between 50-keV protons and noble gases as a function of the projectile scattering angle. The coincidences are dominated by capture to the 2p state of the projectile. While the total cross sections depend strongly on the target, the shape of the angular distribution of the differential cross sections was found to depend only weakly on that parameter. The data indicate that electrons are captured predominantly from the outermost shell of the target atom for the collision systems studied here. PACS numberk): 34.70. + e, 34.50.Fa ©1992
Measurements of elastic angular differential cross sections have been carried out for four quasi-one-electron collision systems at intermediate energies.
in a two-level system for SF 6 .The pulse-delay times shown in Fig. 3 refer to the intensity peaks; they cannot be accounted for theoretically, even if we were dealing with SIT in a two-level system, since the dephasing collision times and laser-pulse durations were of the same order of magnitude in our studies. We find a decrease in delay time with decreasing chlorine pressure at constant total values of p C \ 2 corresponding to a decrease in pulse-delay time with increasing dephasing collision frequency (see Fig. 3).We did not observe multiple-pulse formation and nearly complete transparency, perhaps because of relatively poor laser-beam quality. Gibbs and Slusher 7 showed in studies of SIT for a two-level system that, for a single-mode laser output, the intensity distribution must be uniform in order to allow observation of multiple pulses and peak amplification.In conclusion, we re-emphasize the fact that we are dealing with a "pseudo-two-level" system since the upper state in the bound-free transitions is unstable in times of the order of 10" 12 sec. The fact that anomalous transmission is nevertheless observed must indicate that nonlinear interactions with the coherent radiation field take place on a similar time scale, thereby producing excessive transparency in a kind of lossy system. The detailed nature of this problem Energy analysis of fast ions after collision has recently been employed to study excitations of atoms, molecules, and ions. 1 " 3 Park and Schowengerdt 4 describe the apparatus employed in the present study. Modifications have improved energy resolution and facilitated data handling, 5 but have not altered the basic technique.The ion N + is of interest in astrophysics and atmospheric physics. The forbidden transition 2p 2l D~2p 23 P at 6584 A is used extensively for clearly requires theoretical study.determination of electron temperature and degree of ionization in nebulas. 6 " 8 This transition and i-the forbidden transition 2p 2 X S^ 2p 2 l D at 5755 A are also observed in aurora and airglow and are employed in understanding these phenomena. 9 ' 10 Beam-foil spectroscopy measurements of lifetimes of excited N + states, 11 electron impact ionization of N + , 12 and emission lines of N + from electron impact on N 2 , 13 have been reported.The apparent differential (energy-loss) crossThe excitation spectrum of N + has been observed by examining the energy lost by a 50-keV N + beam passing through a He target. The spectrum exhibits dramatic features with large cross sections. Determination of the approximate ratio of metastable to groundstate ions in the primary ion beam has permitted measurement of excitation cross sections from both ground-state and metastable N* ions colliding with He target atoms. 397
Ion Energy Loss Spectrometry has been applied to the measurement of cross sections differential in both scattering angle and ion energy loss. Differential cross sections obtained for excitation of the n=2 level of atomic hydrogen by various ions provides unexpectedly good agreement with the available theories. IntroductionThe justification for the application of the various approximations used in theoretical studies of ion-atom collisions is largely based on the meager data available for proton-atomic hydrogen collisions. Atomic hydrogen is extremely difficult to handle in precision experiments and as a result very few experiments have been performed. The UMR ion energy-loss
Experimental studies have been made of superelastic and inelastic collision processes involved in the state-selective single-electron capture reaction 'He2 ' +He( 1 ' S )--'He '(n J-k He+( n ' ), where n and n 'are the final principal quantum-number states of the collision products. Total cross sections have been measured at projectile energies of 15, 30, and 45 keV/u, by examining the energy loss-gain of the fast 3He-product ions, for the superelastic n = n ' = I channel, and for the sum of the inelastic n = 2 , n ' = 1 and n = 1, n1=2 states. Measurements are also presented for Ne and Ar targets.
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