Spectroscopic resolution

Within a few exceptions, all singlet states can be correlated to an observed experimental feature. Especially, the high density of states around 11.8 and 12.7 eV is compatible with the observation of unresolved broad peaks in the 11.6-11.9 eV and 12.5-12.8 eV spectral intervals [60], Unfortunately, the lack of spectroscopic resolution makes any unambiguous one-to-one assignment impossible in these regions. 

As an example of the application of the solid-state methods described above, we show the spectra of the naphthalene radical cation in different media236 (Figure 26). Note the increase in spectroscopic resolution and the extension of the range of observation into the UV when using argon matrices. 

The Fermi-distribution factor in Eq. (14.2), imposes another limit on spectroscopic resolution. At room temperature, ksT. Ol eV. The spread of the energy distribution of the sample is IkeT O.OSl eV. The spread of the energy distribution of the tip is also IksT O.OSl eV. The total deviation is LE AkeT OA eV. 

Feshbach or compound resonances. These latter systems are bound rotovibra-tional supramolecular states that are coupled to the dissociation continuum in some way so that they have a finite lifetime these states will dissociate on their own, even in the absence of third-body collisions, unless they undergo a radiative transition first into some other pair state. The free-to-free state transitions are associated with broad profiles, which may often be approximated quite closely by certain model line profiles, Section 5.2, p. 270 If bound states are involved, the resulting spectra show more or less striking structures pressure broadened rotovibrational bands of bound-to-bound transitions, e.g., the sharp lines shown in Fig. 3.41 on p. 120, and more or less diffuse structures arising from bound-to-free and free-to-bound transitions which are also noticeable in that figure and in Figs. 6.5 and 6.19. At low spectroscopic resolution or at high pressures, these structures flatten, often to the point of disappearance. Spectral contributions of bound dimer states show absorption dips at the various monomer Raman lines, as in Fig. 6.5. 

The HREELS, Auger electron spectroscopy (AES) and thermal desorption spectrometry (TDS) experiments were carried out in a UHV chamber described previously.6 Briefly, the chamber was equipped with a HREELS spectrometer for vibrational analysis, a single-pass cylindrical mirror analyzer for AES measurements and a quadrupole mass spectrometer for TDS measurements. The HREELS spectra were collected in the specular direction with an incident energy of 3.5 eV and with a spectroscopic resolution of 50-80 cm-1. The TDS data were obtained by simultaneously monitoring up to 16 masses, with a typical heating rate of about 1.5 K s-1. 

Line broadening processes are important in themselves, in the information they can provide concerning the important physics of a molecular gas system. They are also important to the experimental spectroscopist in determining the spectroscopic resolution and hence the amount and accuracy of the information which can be derived. We here review briefly the principal effects which determine spectroscopic line widths in different experiments. 

The Doppler effect plays a major role in spectroscopic resolution, in both beam and nonbeam experiments. The sonic form of the Doppler shift, when a moving vehicle emits a sound heard by the stationary observer, is familiar to everyone. The electromagnetic radiation equivalent can be expressed in a very simple form. If a molecular source is moving with a velocity v relative to a receiver, and is emitting radiation of frequency v, the observed frequency / is given by... 

R, (1) exchange ratio, k/Av(), (2) absolute configuration at a chiral center (3) spectroscopic resolution (4) ideal gas constant ROI, region of interest... 

Eq. (3.6)]. The total length of time that the FID signal is monitored is called the acquisition time ( acq). which is inversely related to the spectroscopic resolution [Eq. (3.8)]. 

Fig. 7. Picosecond kinetics of flash-induced absorbance changes at 432 and 380-390 nm in PS-1 core complex [PTOO-AqA,] isolated from Synechocystis sp. PCC 6803. Figure source Brettel and Vos (1998) Spectroscopic resolution of the picosecond reduction kineticsofthe secondary electron acceptor in photosystem I. FEBS Lett 447 316.

K Brettel and MH Vos (1999) Spectroscopic resolution of the picosecond reduction kinetics of the secondary electron acceptor in photosystem I. FEES Lett 447 315-317... 

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