Helium photoionization spectrum

The apparatus has been already described in Ref. [7]. The clusters are produced by laser vaporization of a sodium rod, with helium at about 5 bars as a carrier gas and a small amount of SF6. The repetition rate is 10 Hz. In this configuration, the vibrationnal temperature of the formed clusters is roughly 400 K,[10] that gives 85% of C2V geometry and 15% of C3V for a Boltzman distribution. The laser beams are focused onto the cluster beam between the first two plates of an axial Wiley Mac-Laren Time-Of-Flight mass spectrometer with a reflectron. The photoionization efficiency curve as well as the photoabsorption spectrum determined by a photodepletion experiement are displayed on Fig. 1(b) and 1(c) respectively. The ionization threshold is at 4.3 eV, close to the 4.4 eV calculated for the C3V isomer and 4.9 eV for the C2V isomer (see the Fig. 1 (b)). The conclusion arising out of the photodepletion spectrum shown on Fig 1(c) and from ab initio calculations of the excited states, [5] is that the observed... 

Figure 4.37 Spectrum of electrons ejected from helium after photoionization with mono-chromatized Al Ka radiation. The main Is photoline and (magnified by a factor of 20) discrete (n = 2, 3,4) and continuous satellites (above the threshold indicated at 79 eV) are shown as well as structures resulting from the inelastic scattering of Is photoelectrons in the source volume. Reprinted from J. Electron Spectrosc. Relat. Phenom. 47, Svensson et al., 327 (1988) with kind permission from Elsevier Science - NL, Sara Burgerhartstraat 25, 1005 KV Amsterdam, The Netherlands.

In vacuum ultraviolet photoelectron spectroscopy (UPS), the sample atom or molecule is exposed to radiation in the vacuum ultraviolet region of the electromagnetic spectrum. A readily available source of radiation is the helium discharge lamp, whieh produces a sharp Hel line at 21.2 eV. Since the energy required for photoionization of sets of valence electrons is in the vicinity of 6 eV to this energy, we obtain a polyenergetic emission of electrons described by the Einstein relation... 

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