Linewidth and lifetimes

The occurrence of predissociation opens up a new family of observable quantities. It is possible to measure not only linewidths or lifetimes, but also the internal state distributions of the fragments. All these quantities are sensitive to the intennolecular potential and can be used to test or refine proposed potential surfaces. 

Another method for lifetime determination uses the level-crossing technique 12 t) which measures the natural linewidth (and with it the lifetime) from the change of the spatial fluorescence intensity distri-... 

Brillouin scattering of laser light in liquids has been studied by several authors. Shapiro etal. 233) measured hypersonic velocities in various liquids and obtained a Brillouin linewidth of 0.011 cm" in methylene chloride but of less than 0.002 cm in benzene, carbon disulfide and chloroform. The broadening of the Brillouin components arises from damping of thermal phonons and is closely connected with the viscosity coefficient of the medium. From the measured linewidths, the lifetimes of the phonons responsible for Brillouin scattering at 89 45 were calculated to be 4.8 x 10 sec for methylene chloride and 7.6 x 10 sec for toluene. 

A further factor which affects the shape of a resonance line is the transport of resonance radiation through the. parent gas. Milne s early theory of self-absorption by the imprisonment of resonance radiation has been revised by Holstein (3) and Bichermau (4), taking into account the incoherent scattering of resonance photons. Furthermore, Walsh (" ) has extended the imprisonment lifetime calculation for cases where Doppler and collision broadening of the resonance line are simultaneously present, and in addition this author has examined the complications caused by the, hfs. The line shape, linewidth, and other properties of self-absorbed lines hare been discussed recently bv Tako (6), who summarizes the various effects of self-absorption as follows ... 

Once the parameters are determined, we can calculate other spectroscopic properties for the 4f 15d configuration. These include emission spectra and lifetimes, the presence (or lack of) emission from the 4f 15d configuration, and non-radiative relaxation effects upon the linewidths of 4f 15d and 4F excited states. 

Although there are only 22 cases listed In Table I, the variety Is great enough to permit several questions to be answered with regard to the correlation of the linewidth-derlved lifetime of the initial state with various structural and dynamical features. First, it Is Important to observe that the total range of lifetimes for these systems Is remarkably small — about 0.4 to 4 ps for molecule-molecule systems and 1.8 to 11 ps for atom-molecule systems. With this In mind, let us examine several parameters which one might expect to be correlated with the lifetime. 

The deperturbation models provide a uniform explanation of level patterns, transition intensities (Chapter 7), radiative lifetimes, linewidths, and systematic variations of coupling matrix elements with quantum numbers. 

The 93-26-keV excited state of Zn has a lifetime of 9400 ns. This gives an unusually narrow Mossbauer linewidth of = 3T2 x 10 mm s. The potentially high precision which this offers promised spectacular results in measurements of, for example, the gravitational red-shift. However, the normal level of acoustic vibrations in the laboratory is greater than the natural linewidth, and consequently the first attempts to observe the resonance were unsuccessful [13]. 

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