Calcium atomic beam

They are focused onto a Calcium atomic beam (laser beam waists about 50 jjm). ... 

Reactions within a van der Waals (vdW) complex of calcium with hydrogen halides (HC1 and HBr) lead to electronically excited calcium halides. These reactions have been quite extensively studied in full collisions of excited calcium beams (Brinckmann et al. 1980 Brinckmann and Telle 1977 Rettner and Zare 1981, 1982 Telle and Brinckmann 1990). The electronic excitation of the calcium atom results in a strong chemiluminescence under collisional conditions. The efficiency of this chemiluminescence depends upon the electronic state and the fine structure component, and the final product state is influenced by the preparation conditions of the collision. In the reaction Ca(4s4p1P1) + HC1, the direction of the polarization of the P orbital with respect to the collision relative velocity (pK or pff) has an effect on the branching ratio to the products CaCl, A2n or B2X+ (Rettner and Zare 1981, 1982). 

Fig. 9.62 Ramsey resonances of the calcium intercombination line at X = 657 nm, measured in a collimated Ca atomic beam ...

Fig. 14.43a,b. Ramsey resonances of the calcium intercombination line at A. = 657 nm, measured in a collimated Ca atomic beam (a) Doppler profile with a reduced Doppler width and a central Lamb dip, if only one interaction zone is used (b) expanded section of the Lamb dip with the two recoil components observed with three interaction zones with separations L = 3.5 cm and L = 1.7 cm. The dashed curves show results with partial suppression of one recoil component [14.114]... 

An example where nonlinear phenomena in connection with laser-rf spectroscopy have been used in atomic beams, is the recent work on calcium isotopes carried out in our laboratory. The goal of these experiments was to determine nuclear electric quadrupole moments from precise hyperfine structure data of the atomic spectrum. This is of some importance in the case of calcium, since Ca as well as Ca are so-called double-magic nuclei, i.e., with closed proton and neutron shells. Radioactive Ca (t = 1.03 X 10 yr) and the stable isotope Ca have been investigated by laser-rf spectroscopy. The measurements allow to study the influence of a single neutron and three neutrons, respectively, on the double-magic °Ca core. 

A similar scheme was used for the spectroscopic studies on hyperfine components and isotope shifts of rare stable isotopes of calcium and the radionuclide Ca. Calcium atoms in an atomic beam were excited with single-frequency cw dye and titanium sapphire lasers and then photoionized with the 363.8 nm or 514.5 nm line of an Ar laser. 

The reaction of excited calcium atoms with HCl has been widely studied in beam gas experiments (i3-, and Rettner et al( ) have shown that the Ca P + HCl reaction is sensitive to the orientation of the calcium orbital with respect to the relative velocity in the collision. This reaction produces Ca Cl (A,B) with a high cross section 60... 

Our basic apparatus is shown in Fig. 1, except that the polarization accessories are not immediately required. A primary beam of calcium atoms is produced by resistively heating an oven (nozzle diameter about 0.7 mm) to approximately 1400 K. A DC discharge between a ring electrode in front of the nozzle and the nozzle exit serves to excite approx. 20% of the atoms into metastable states [9]. After coUimation, this beam enters the collision zone and impinges on a secondary gas. 

X-ray fluorescence A method of analysis used to identify and measure heavy elements in the presence of each other in any matrix. The sample is irradiated with a beam of primary X-rays of greater energy than the characteristic X-radiation of the elements in the sample. This results in the excitation of the heavy elements present and the emission of characteristic X-ray energies, which can be separated into individual wavelengths and measured. The technique is not suitable for use with elements of lower atomic number than calcium. 

Strontium may be included in the diluent to be used as an internal standard with double-beam spectrophotometers. The signal from calcium is referenced to the simultaneously measured strontium signal, thereby reducing variability caused by fluctuations in the flame and atomization rate. 

A burner head, typically with a single slot (10 x 0.2 cm), is aligned along the axis of the optical beam from the radiation source. The nebuliser/burner assembly is mounted on a platform which provides for positional adjustment in both the vertical and horizontal planes. The optimal height of the optical beam above the burner slot varies with each analyte element (and somewhat with the sample composition) is established experimentally for each standard solution. An impressive graphic presentation of the spatial distribution of analyte atoms of sodium, calcium, or molybdenum in an air/C2H2 flame (under identical operating conditions) has been presented by Rann and Hambly Anal. Chem. 37, 880, 1965). 

The breakthrough experiment was carried out by Whitham et al. [39,40] in France. They used a Smalley-type laser vaporization source (Fig. 4) to provide a molecular beam of Ca atoms entrained in He or Ar gas. The second harmonic (532 nm) from a pulsed Nd YAG laser was focused (Fig. 4) on a rotating calcium rod. About 500 jus prior to this, a pulsed valve (left side of Fig. 4) is opened and the plume of vaporized metal is entrained in Ar or He gas. The carrier gas is seeded with a few percent of the oxidant such as H20. The plume of excited- and ground-state metal atoms are carried down a short channel and react with the oxidant. At the end of the channel, the product molecules such as CaOH expand into the vacuum chamber and cool. After a short expansion, the pressure has dropped so low that the molecules are effectively in a collisionless, ultracold (<10K) environment. 

A much mure troublesome problem occurs when Ihe source of absorption or scattering originates in Ihe sample matrix. In this instance, the power of the transmitted beam P is reduced by the matrix components, but the incident beam power Pq is not a positive error in absorbance and thus concentration results. An example of a potential matrix interference because of absorption occurs in the determination of barium in alkaline-earth mixtures. As shown by the solid line in Figure 8-8, the wavelength of Ihe barium line used for atomic absorption analysis appears in Ihe center of a broad absorption band for CaOH. We therefore anticipate that calcium will interfere in barium determinations, but the effect is easily eliminated by substituting nitrous oxide for air as Ihe oxidant. The higher temperature of the nitrous oxide flame decomposes the CaOH and eliminates Ihe absorption hand. 

Co-condensates between metallic samarium and 4-pentyl-4 -cyanobiphenyl (5CB) in the solid phase have been obtained via joint atomic/molecular beam deposition on a cooled calcium fluoride surface at liquid nitrogen temperature (Shabatina et al., 2000, 2001, 2005). The film samples have been studied by IR and UVA IS spectroscopy in the temperature range from 80 to 300 K. Two types of complexes were detected, one complex with a metal to ligand... 

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