Charge-cloud distribution

Figure 30. Schematic charge-cloud distribution of atomic />-state excited by linearly polarized light with electric vector EA . Different relative alignments of Eh lead to Ict), ) states with respect to fixed coordinate frame.

Fig. 9.7. Schematic of the angular dependence of a charge-cloud distribution of an atomic state excited by polarised electrons. The tilt (e) out of the scattering plane must by parity conservation be zero if = 0.

P4 is again a Stokes parameter for unpolarised electrons. P5 and Pe must be zero if Px = 0. This can be seen by taking a mirror reflection in the scattering plane. Nonzero values of P5 and Pe would violate parity conservation if Px = 0, since the electron beam geometry would remain unchanged unless there is an x-component of Pe. Similarly the tilt (e) in the charge-cloud distribution out of the scattering plane indicated in fig. 9.7 must vanish unless Px 0. 

Fig. 9.11. Normalised charge-cloud distribution of the excited Hg (6 Pi) state after collision with 8 eV electrons scattered through 20°. For Pg = 0 and Pe = Py = +1 the view is perpendicular to the scattering plane (3 direction), and for Pg = Px = +1 the view is in the scattering plane from the —x direction (fig. 9.7) (from Hanne, 1992).

It can be seen that electron—photon coincidence experiments with polarised electrons permit the investigation of spin effects in electron impact excitation of atoms at the most fundamental level. It can lead to direct information on both exchange effects and spin—orbit effects in the excitation mechanism. The information on the population of the magnetic sublevels can be visualised by charge-cloud distributions. These can tilt significantly out of the scattering plane for incident electrons transversely polarised in the scattering plane. 

Dispersion forces n. (1) Weak forces between atoms or molecules due to momentary fluctuations in their electronic charge-cloud distributions. (2) The force of attraction between molecules possessing no permanent dipole. The interaction energy is given by... 

Molecular orbital (MO) (1932) n. An electronic energy level in a molecule and the corresponding charge-cloud distribution in space. 

Volume of vessel (free volume V) Shape of vessel (area and aspect ratio) Type of dust cloud distribution (ISO method/pneumatic-loading method) Dust explosihility characteristics Maximum explosion overpressure P ax Maximum explosion constant K ax Minimum ignition temperature MIT Type of explosion suppressant and its suppression efficiency Type of HRD suppressors number and free volume of HRD suppressors and the outlet diameter and valve opening time Suppressant charge and propelling agent pressure Fittings elbow and/or stub pipe and type of nozzle Type of explosion detector(s) dynamic or threshold pressure, UV or IR radiation, effective system activation overpressure Hardware deployment location of HRD suppressor(s) on vessel... 

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