Scattering signals, angular

Figure 2. Light of incident angular frequency o>0 is scattered from two particles undergoing random Brownian motion. Because the scattered light is Doppler shifted by the two particles respectively, the scattered signal contains two discrete frequencies.

However, quantitative analysis is more complicated. We [4.10,11] have recently given theoretical arguments to show that the angular distribution, intensity, and polarization of the Raman or fluorescent scattering signal will not only depend upon the number of active molecules but also upon the particle size, shape, refractive index, internal structure, and the distribution of the active molecules within the particle. This will be illustrated in this chapter by representative calculations. 

A molecular beam scattering experiment usually involves the detection of low signal levels. Thus, one of the most important considerations is whether a sufficient flux of product molecules can be generated to allow a precise measurement of the angular and velocity distributions. The rate of fonnation of product molecules, dAVdt, can be expressed as... 

The energy analysis of these inelastically scattered electrons is carried out by a cylindrical sector identical to the monochromator. The electrons are finally detected by a channeltron electron multiplier and the signal is amplified, counted and recorded outside of the vacuum chamber. A typical specularly reflected beam has an intensity of 10 to 10 electrons per second in the elastic channel and a full width at half maximum between 7 and 10 meV (60-80 cm l 1 meV = 8.065 cm-- -). Scattering into inelastic channels is between 10 and 1000 electrons per second. In our case the spectrometer is rotatable so that possible angular effects can also be studied. This becomes important for the study of vibrational excitation by short range "impact" scattering (8, 9, 10). 

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