Combining a tunable single mode laser -atomic beam photoelectron source with a skimmed supersonic beam target we have carried out ultrahigh resolution studies of threshold electron attachment to SF 6 molecules. Monitoring SF 6 2 formation around the onset for field ionization of high n Rydberg atoms, residual electric fields are diagnosed and reduced to levels around 0.01 V͞m, allowing the first study of free electron attachment cross sections s͑E͒ for energies down to about 20 meV at energy widths as low as 20 meV. The present results for SF 6 2 production conclusively demonstrate the convergence towards the limiting s-wave attachment behavior s~E 21͞2 at energies below 1 meV.[S0031-9007(98)06711-8] PACS numbers: 34.80.Lx, 34.60. + z, 82.30.Fi The attachment of slow electrons to molecules(1) with formation of long-lived negative ions XY 2 or dissociated products X 2 1 Y (dissociative attachment) is an important process in gaseous dielectrics [1,2]. Many halogen-containing molecules such as SF 6 and CCl 4 exhibit very large electron attachment cross sections at low energies, and it is of both fundamental and applied interest to study the threshold behavior ͑E ! 0͒ with high resolution. For sufficiently short-ranged interaction potentials ͓V ͑r͒~r 2m , m . 2͔, capture of particles with orbital angular momentum L is theoretically predicted to exhibit a threshold energy dependence s͑E͒~E L21͞2 [3,4]. For s-wave attachment ͑L 0͒ one therefore expects a diverging cross section s͑E; L 0͒~E 21͞2ỹ 21 , as also observed for neutron capture by nuclei at low velocities y [3]. Using a vacuum ultraviolet photoelectron attachment technique with an energy resolution around DE ഠ 6 meV (FWHM) Chutjian and coworkers provided evidence for s-wave attachment to occur in several systems including SF 6 and CCl 4 [2,5]. Electron transfer studies with laser excited, state selected Rydberg atoms A ‫ءء‬ ͑nl͒, most notably those by Dunning and colleagues [6,7], demonstrated that the rate coefficient for Rydberg electron attachment ͓ f nl ͑y͒ velocity distribution of nl Rydberg electron͔is essentially constant at high principal quantum numbers ͑n . 40͒ for several molecules including SF 6 and CCl 4 as expected for s-wave attachment. Using a novel laser photoelectron attachment (LPA) method, Klar et al. investigated free electron attachment processes with sub-meV resolution [8][9][10][11]. Their results clearly indicated that the limiting E 21͞2 dependence is reached only at very low energies ͑#1 meV͒; moreover, they detected cusp structures at onsets for vibrational excitation [8,9].At these low energies the major problem is associated with the influence of residual electric fields in the reaction volume. Klar et al. [9,10]-using time-delayed ion extraction following pulsed electron attachment at high repetition rate-carried out model calculations for the effective energy dependence of negative ion formation, taking into account the effects of a homogeneous residual field (of fitted strength) on the electron trajectories. In this way they...

Using transverse resonant two-photon CW laser excitation of metastable 40Ar(4s 3P2) atoms in a collimated beam via the Ar(4p 3D3) level, we have carried out a comprehensive high-resolution study of odd Ar(2P3/2 ns,nd,J = 2,3) Rydberg states (n = 13-90). The transition energies are determined with an uncertainty of 0.006 cm-1 and perturbations in the spectra associated with the Ar(2P1/2 8d´9d´J = 2,3) levels are clearly detected. Moreover, the low-lying Ar(nd´J = 2,3) autoionization resonances (n = 10-14) have been investigated and the respective widths (ranging from 5000 to 26 000 cm-1) determined. A very sharp resonance (reduced width 27 cm-1) has been detected and identified as a member of the ng´,J = 3 series. A multichannel quantum defect theory (MQDT) analysis of the measured bound Rydberg levels yields reliable eigenchannel quantum defect parameters which describe the odd J = 2 and 3 spectra of Ar in the bound as well as in the autoionization region. The MQDT-derived widths for the nd´ resonances are found to be in good agreement with the experimental results. The s-d coupling observed in the J = 2 spectrum is discussed in detail.

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Articles you may be interested inX-ray photoelectron spectroscopy study on the chemistry involved in tin oxide film growth during chemical vapor deposition processes J. Vac. Sci. Technol. A 31, 01A105 (2013); 10.1116/1.4756898 New insight brought by density functional theory on the chemical state of alaninol on Cu(100): Energetics and interpretation of x-ray photoelectron spectroscopy data J. Chem. Phys. 128, 114709 (2008); 10.1063/1.2888562 X-ray photoelectron spectroscopy study of self-assembled monolayers of alkanethiols on (001) GaAs Novel cyanoterphenyl self-assembly monolayers on Au(111) studied by ellipsometry, x-ray photoelectron spectroscopy, and vibrational spectroscopies J. Chem. Phys. 122, 224707 (2005); 10.1063/1.1893618 1-octadecene monolayers on Si(111) hydrogen-terminated surfaces: Effect of substrate dopingA series of para-substituted, halogenated (F, Cl, Br, and I) benzoic acid monolayers were prepared on the native oxide of aluminum surfaces by solution self-assembly and spin-coating techniques. The monolayers were characterized by x-ray photoelectron spectroscopy (XPS) and water contact angles. Several general trends are apparent. First, the polarity of the solvent is critical to monolayer formation. Protic polar solvents produced low coverage monolayers; in contrast, nonpolar solvents produced higher coverage monolayers. Second, solution deposition yields a higher surface coverage than spin coating. Third, the thickness of the monolayers determined from XPS suggests the plane of the aromatic ring is perpendicular to the surface with the carboxylate functional group most likely binding in a bidentate chelating geometry. Fourth, the saturation coverage ($2.7 Â 10 14 molecules cm À2 ) is independent of the para-substituent.

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