Fine structure changing collisions

Highly polar molecules, such as HC146 and NH334 have very large mixing cross sections, as shown by Stebbings et al. It is not clear whether the polar molecules interact with only the electron of the Rydberg atom or with the atom as a whole. 

All of the above observations are consistent with interpreting fine structure changing collisions in Rydberg atoms as elastic e -perturber scattering leading to 

Many n changing cross sections have been measured. For example, the depopulation of the Na ns states by several rare gases has been studied over a wide range of n values.52-54 To convey the essential ideas, though, it is useful to consider a single set of measurements, the depopulation cross sections of Rb Rydberg states with He. In Fig. 11.8 we show the energy levels of Rb.50 The s, p, and d states all have substantial quantum defects, and the f states have a quantum 

The cross sections for depopulation of the mixed pair of ml fine structure levels are much smaller, as shown by Fig. 11.9. The low n, 15, cross sections, measured by fluorescence detection, rise to their maximum of 130 A2 at n — 15,50 and the higher n cross sections, measured using field ionization, decrease from 118 A2 at n = 30 to 59 A2 at n = 41.55 Although there are no measurements for 15 n 30, from the data in Fig 11.9 it is hard to imagine that the cross section ever exceeds 

The np state depopulation cross sections were all measured using fluorescence detection, and as a result the highest n observed is n = 22.26 As shown by Fig 11.9, the cross sections rise to a plateau of 60 A2, a value distinctly smaller than the cross sections for any other ni states. 

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Scattering has been measured for Ne + Ne, Ar + Ar, and Dr + Kr by different groups at thermal energies, but no data and potentials have been published so far, as the analysis is quite involved. First, it is impossible to quench one of the two metastable states without an expensive laser, so that an investigator is generally forced to work with mixtures and second, six potentials contribute coherently for the dominant 3P2 species. The cross sections for fine-structure changing collisions are small78 80 and hence can... 

There have been many experimental studies on fine structure changing collisions with argon ions, most of which have been performed at collision energies high in comparison to the excitation energy of the Pi/2 state. With the exception of the following unpublished data, which are from the PhD thesis of E. Haufler there have been so far no experimental studies determining the fine structure relaxation... 

The presence of overcrowding in triphenylene has been demonstrated by Clar (1950) from an examination of the absorption spectra at 18°C and — 170°C. At — 170°C the / -band spectra of such aromatic hydrocarbons as benzene, naphthalene, anthracene, and pyrene become more distinct, showing much more fine structure than at 18°C. This is explained by the cessation at low temperature of thermal collisions which produce molecular deformations, thereby improving the definition of the molecular electronic orbitals. Where this change in spectra does not occur, permanent deformation at both low and high temperatures... 

Collision-induced transitions between fine-structure components where the relative orientation of the electron spin with respect to the orbital angular momentum is changed have been studied in detail by laser-spectroscopic techniques [13.64]. One of the methods often used is sensitized fluorescence, where one of the fine-structure components is selectively excited and the fluorescence of the other component is observed as a function of pressure [13.65]. Either pulsed excitation and time-resolved detection is used [13.66] or the intensity ratio of the two fine-structure components is measured under cw excitation [13.67]. 

In Ref. 51, the relative population of the 0( Pj = 2,1,0) product fine-structure states were determined at different collision energies. The energy dependence in the change of the population of the 0( Pj = 2 l,o) fine-structure states from a diabatic one at Ec.m. = 1.6 eV to an adiabatic one at fec.m. = 2.5 eV was attributed to a reduction of nonadiabatic coupling in the exit channel due to the increase of translational energy released to the O + OH products with increasing collision energy [46g]. 

The simplest vibrational spectra are obtained for molecules isolated in a matrix of a condensed inert gas, for which very sharp peaks are usually observed (Figure 8.7(d)). In all other phases the peaks are broadened and/ or split, but for different reasons. In the gas phase, changes in rotational quantum numbers accompany the vibrational transitions for gases (Section 8.6.2). At high resolution, these result in fine structure at lower resolution, various band envelopes, some of them characteristic, can be observed (Figure 8.7(a)). We find these only in the spectra of gases because rotation is not quantized in condensed phases, because the rate of intermolecular collision is greater than the rotation rate. 

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