By Wolfgang Demtröder

This creation to Atomic and Molecular Physics explains how our current version of atoms and molecules has been built over the past centuries either through many experimental discoveries and, from the theoretical facet, by way of the advent of quantum physics to the sufficient description of micro-particles. It illustrates the wave version of debris via many examples and exhibits the boundaries of classical description. The interplay of electromagnetic radiation with atoms and molecules and its capability for spectroscopy is printed in additional aspect and specifically lasers as sleek spectroscopic instruments are mentioned extra completely. Many examples and issues of suggestions are provided to inspire readers to actively interact in experimentation.

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The quantity ξ 2 , which is a measure of the mean deviation of a particle from its original location at time t = 0 increases during √ the time interval ∆t only with the square root ∆t. 46). 12]. A modern version of it is shown in Fig. 20a. A small mirror is suspended on a thin torsional wire. The air molecules impinge on the mirror surface and cause, by their momentum transfer, small statistical angular deviations ∆ϕ of the mirror from its equilibrium position at ϕ = 0, which can be monitored by the reﬂection of a laser beam, detected with a position-sensitive CCD detector.

25) Electron beam like that in the ﬁeld emission microscope. The emitted Fig. 25. Field-emission electron source where the electrons electrons can than be imaged by the electron optics to are emitted from a point-like tungsten tip and imaged by form a nearly parallel beam that traverses the sample. electrostatic lenses Each point of the sample is then imaged with a large magniﬁcation onto the screen. The drawbacks of the transmission electron • The electron beam has to be intense in order to obtain sufﬁcient image quality with a high contrast.

Can One See Atoms? velocity components within the interval vx to vx + dvx . 30) p = n 2m v2x = nm v2x , 2 where n is the total number density. 29) v2x = v2y = v2z = 1 2 v . 32) where E kin = (m/2)v2 is the mean kinetic energy of each molecule. Using the relation n = N/V this can also be written as 2 p = n · E kin . 33) 3 Many experiments have proved that the product pV at a constant number N of molecules in the volume V solely depends on the temperature T . This means that the mean kinetic energy of the molecules is a function of T .