Line width mechanisms

The width and shape of the energy loss peaks in HREELS are usually completely determined by the relatively poor instrumental resolution. This means that no information can be obtained from HREELS about such interesting chemical physics questions as vibrational energy transfer, since the influence of the time scale and mechanism of vibrational excitations at surfaces on the lifetimes, and therefore the line widths and shapes, is swamped. (Adsorbates on surfaces have intrinsic vibra-... 

Both of the current models for the central mode scattering contain the implicit assumption of cubic symmetry above Tm. Possibly because of the dramatic nature of the soft-mode behaviour and a ready understanding of the structural transformation in terms of it, there was a strong incentive to establish a link between it and the central mode scattering. A consistent difficulty with this approach is the failure to establish an intrinsic line-width for the central mode peak and the unspecified nature of the mechanism responsibly for a low-frequency resonance in the energy of the soft mode. ... 

B. Studies of Equilibria and Reactions.—N.m.r. spectroscopy is being increasingly employed to study the mode and course of reactions. Thus n.m.r. has been used to unravel the mechanism of the reaction of phosphorus trichloride and ammonium chloride to give phosphazenes, and to follow the kinetics of alcoholysis of phosphoramidites. Its use in the study of the interaction of nucleotides and enzymes has obtained valuable information on binding sites and conformations and work on the line-widths of the P resonance has enabled the calculation of dissociation rate-constants and activation energies to be performed. 

Line-width of XRD peaks of these acidic Cs salts (x = 2.1. 2.2, and 2.5) show that the size of the primary crystallites was about 120 A and the primary crystallites themselves are nonporous [29]. Therefore, the pores observed in the present study correspond to the interparticle voids (not intraparticle). The pore structure and the mechanism of the formation of pores will be discussed in our forthcoming paper. 

Perhaps the first evidence for the breakdown of the Born-Oppenheimer approximation for adsorbates at metal surfaces arose from the study of infrared reflection-absorption line-widths of adsorbates on metals, a topic that has been reviewed by Hoffmann.17 In the simplest case, one considers the mechanism of vibrational relaxation operative for a diatomic molecule that has absorbed an infrared photon exciting it to its first vibrationally-excited state. Although the interpretation of spectral line-broadening experiments is always fraught with problems associated with distinguishing... 

Abstract Sonoluminescence from alkali-metal salt solutions reveals excited state alkali - metal atom emission which exhibits asymmetrically-broadened lines. The location of the emission site is of interest as well as how nonvolatile ions are reduced and electronically excited. This chapter reviews sonoluminescence studies on alkali-metal atom emission in various environments. We focus on the emission mechanism does the emission occur in the gas phase within bubbles or in heated fluid at the bubble/liquid interface Many studies support the gas phase origin. The transfer of nonvolatile ions into bubbles is suggested to occur by means of liquid droplets, which are injected into bubbles during nonspherical bubble oscillation, bubble coalescence and/or bubble fragmentation. The line width of the alkali-metal atom emission may provide the relative density of gas at bubble collapse under the assumption of the gas phase origin. 

To understand the molecular mechanism of phototropism it is essential to know whether adaptation is localized in a defined region of the cell or whether it is spread throughout the cell. To determine this Delbriick and Vaiju (1961) performed a series of experiments in which they stimulated the sporangiophore with ultraviolet light in sharply bounded and narrow test areas (line width of 0.2 mm). They found that the... 

The 113Cd Ti values estimated for the various peaks varied from 10 to 50 ms and obeyed the qualitative dependence upon 1/R6 (R = Mn-Cd distance) of the dipolar relaxation mechanism expected to be operative. The broad line widths were also shown to have significant contributions from the T2 relaxation induced by Mn++, with both dipolar and contact terms contributing. The 113Cd shifts of the peaks assigned to different shells were measured as a function of temperature, and observed to follow a linear 1/T dependence characteristic of the Curie-Weiss law, with slopes proportional to the transferred hyperfine interaction constant A. 

Water exchange of Pd(H20)4+ has been studied by the O-nmr line width of coordinated water in 0.8-1.7 M HCIO4. The parameters (Table 4.12) support an associative mechanism. The exchange rate is over 10 times faster than for Pt(H20)4+ (Ref. 270). The ligation of... 

Although this equation only applies when the coalescence point is reached, rate constants for the exchange between two or more exchanging sites are accessible by analysis of line widths at half height, Avip, and shift differences, Ar, in Hz. The comparison between the experimental spectrum and the spectrum calculated by use of a simulation package for line shapes provides the mechanism for determining the rate constant of exchange [161, 162]. 

Spin-spin (transversal) relaxation (relaxation time T2) is the second mechanism which is related to molecular mobility. It influences the half-height line widths w [tv = lj(n T2) in the frequency-domain NMR spectrum and is of some relevance in the NMR spectroscopy of quadrupolar nuclei such as, 2H, 14N, 170, 33S and others. In the context of this section, T2 is of very limited relevance. 

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