Atom beams, crossed

The setup used for crossed beam experiments is basically the same apparatus used in the H2O photodissociation studies but slightly modified. In the crossed beam study of the 0(1D) + H2 — OH + H reaction and the H + HD(D2) — H2(HD) + D reaction, two parallel molecular beams (H2 and O2) were generated with similar pulsed valves. The 0(1D) atom beam was produced by the 157 photodissociation of the O2 molecule through the Schumann-Runge band. The 0(1D) beam was then crossed at 90° with the... 

H2 molecular beam. The H-atom products were detected by the Rydberg tagging TOF technique using the same scheme described in the last paragraph with a rotatable MCP detector. Figure 4 shows the experimental scheme of the crossed beam setup for the 0(1D) + H2 reactive scattering studies. The scheme used for the H + D2(HD) studies is very similar to that used in the 0(1D) + H2 except that the H-atom beam source is generated from HI photodissociation rather than the 0(1D)-atom beam source from 02 photodissociation. 

The experimental techniques that have been used to study transition metal atom reactions (crossed molecular beams, flow tubes, etc.) are powerful ones. However, a complete interpretation of the mechanistic and dynamic aspects of these reactions is greatly facilitated through comparison of experimental results to theoretical predictions.159 The early theoretical work by the group of Siegbahn led to a great number of testable predictions, many of which have been found to be remarkably precise. Our measurements of various thermodynamic quantities have shown these calculations to be generally accurate to within 5-6kcal/mol. Unfortunately, due to the... 

Figure 3. Illustration of the cross-beam machine. N is the nozzle source for the molecular beam, C is the buffer chamber with a beam chopper (not shown), H is the hexapole electric field quantum state selector, U are the homogeneous electric field plates, Q is an on-axis quadrupole mass filter, O is the fast atom beam source, and Q and C,8o are channeltrons.

COLLISIONAL ENERGY-TRANSFER SPECTROSCOPY WITH LASER-EXCITED ATOMS IN CROSSED ATOM BEAMS A NEW METHOD FOR INVESTIGATING THE QUENCHING OF ELECTRONICALLY EXCITED ATOMS BY MOLECULES... 

The technique for investigating scattering processes in crossed-beam experiments is well developed. For example, elastic scattering experiments with neutral particles at thermal energies are well understood,85 and the techniques for producing molecular and alkali atom beams and to detect them and interpret their kinematics has been reviewed on several occasions.86, 87. The new aspect of the present work is the technique for... 

Collisional Energy-transfer Spectroscopy with Laser-excited Atoms in Crossed Atom Beams A New Method for Investigating the Quenching of Electronically Excited Atoms by Molecules... 

Fig. 14.13 Experimental arrangement for velocity selecting and focusing the atomic beam. The rotating slotted disc and the pulsed laser beam select atoms in a velocity group, and the hexapole magnet focuses them where they cross the laser beam (from ref. 18).

Fig. 19.6 A schematic view of an apparatus for measuring photoexcitation cross sections and photoelectron energy and angular distributions. The atom beam comes out of the page, and Di and D2 are the electron and ion detector, respectively (from ref. 25).

Here, Hc is the Coulomb-three-body Hamiltonian like Eq. (3), and E is a realvalued energy of the whole system, i.e., the sum of the collision energy and the energy of the target state before collision. For spin-unpolarized positron and atomic beams, the total annihilation cross section is calculated by the statistically weighted average... 

Hyperfine structure measurements using on-line atomic-beam techniques are of great importance in the systematic study of spins and moments of nuclei far from beta-stability. We will discuss the atomic-beam magnetic resonance (ABMR) method, and laser spectroscopy methods based on crossed-beam geometry with a collimated thermal atomic-beam and collinear geometry with a fast atomic-beam. Selected results from the extensive measurements at the ISOLDE facility at CERN will be presented. 

Monoenergetic photons excite a core hole. The modulation of the absorption cross section with energy at 100 - 500 eV above the excitation threshold yields information on the radial distances to the neighbouring atoms. The cross section can be measured by fluorescence as the core holes decay or by attenuation of the transmitted photon beam. EXAFS is one of the many fine -structure techniques. 

We detected the saturated fluorescence emitted by a beam of 23S metastable atoms as they cross at right angle the slave laser light. A 1015 atoms/s.sterad flux of metastable helium atoms was produced by electronic collisions in a DC discharge of a helium atomic beam, similar to that described in [15]. To improve the precision of the linecenter determination, we increased the signal-to-noise ratio S/N by means of standard frequency modulation the third harmonic demodulated lineshape is shown in Fig. 4. The function expected for a Lorentzian spectrum was fit and linecenters were calculated with an uncertainty ranging between 10 kHz and 20 kHz, that is consistent with the observed S/N, mainly limited by the stability of the reference frequency and of the metastable helium beam. The reproducibility was two or three times worse than the uncertainty,... 

Fig. 2. Recent measurements of the Rydberg constant by laser spectroscopy of hydrogen and deuterium. Data points A and B are derived from the wavelength of the Balmer-a [7] or Balmer-8 line [8], observed by quenching of a beam of metastable 2S atoms with crossed dye laser beams. Data C and D are obtained by Doppler-free two-photon spectroscopy of 2S-8..12S transitions, recorded by quenching of a metastable atomic beam [9,10]. The Rydberg values E and F have been measured by Doppler-free two-photon spectroscopy of the 1S-2S transition in a gas cell [11,12],...

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