Sodium excited, from

The excitation transfer has been investigated by studying the sensitized fluorescence of sodium, arising from the decay of several S, P, and D states that have energies close to the excitation energy of the 6 P2 (and 6 P0) state in mercury. Experiments of this type have been reported by the groups of... 

Calcium performs a variety of cellular functions in muscle and nerve that ultimately result in muscular contraction. Excellent descriptions of calcium s function in muscle and nerve are to be found in the reviews by Hoyle (37), Cohen (38), and Robertson (39). At the neuromuscular junction, the excitable cells are very sensitive to changes in extracellular concentrations of calcium. Curtis (40) and Luttgau (41) described a fall in the resting action potential and electrical resistance when the extracellular calcium concentration fell below 10 M. The action potential and electrical resistance returned to normal following addition of calcium to this vitro preparation. The magnitude of the Initial muscle membrane action potential, that which regulates the propagation of further muscle contraction, is also mediated by the extracellular calcium concentration. While the inward flow of sodium ions from the extracellular space remains the dominant factor in the mechanism of muscle membrane depolarization, calcium ion flux appears to mediate the cell s permeability to sodium ions. This effect is particularly true in cardiac tissue (W). 

Figure 24-20 Energy-level diagram for sodium in which the horizontal lines represent the atomic orbitals, which are identified with their respective labels. The vertical scale is orbital energy in electron volts (eV), and the energies of excited states relative to the ground-state 3.S orbital can be read from the vertical axis. The blue lines show the allowed transitions resulting from emission of various wavelengths (in nm), indicated adjacent to the lines. The horizontal dashed line represents the ionization energy of sodium. (Adapted from J. D. Ingle, Jr., and S. R. Crouch, Spectrochemical Analysis, p. 206.

Epilepsy is a neurological disorder characterized by recurrent spontaneous seizures due to an imbalance between cerebral excitability and inhibition, with a tendency towards uncontrolled excitability (Papandreou et al., 2006). Recurrent severe seizures can lead to death of brain cells. Phenytoin (Dilantin, Phenytek) is a widely used anti-seizure medicine (LaRoche, 2007). The primary site of action appears to be the motor cortex where spread of seizure activity is inhibited, possibly by promoting sodium efflux from neurons. Phenytoin tends to stabilize the threshold against hyper-excitability caused by excessive stimulation. The current status of new (second generation) anti-epileptic drugs has been recently reviewed (Bialer et al., 2007). 

The value of E, which can be interpreted as the excitation energy required to move a sodium ion from its normal position in the crystal, is 190 kJ mole". The conductivity remains very low, about 1 X lO" ohm" cm", even at 800°C, only a degree below the melting point. 

Figure 8-4 shows a portion of a recorded emission spectrum for sodium. Excitation in this case resulted from spraying a solution of sodium chloride into an oxyhydrogen flame. Note the very large peak at the far right, which is off scale and corresponds to the 3p to 3s transitions at 589.0 and 589.6 nm (5890 and 5896 A) shown in Figure 8-1 a. The resolving power of the monochromator used was insufficient to separate the peaks. 

The transition of the sodium atom from the excited state 1s 2s 2p 3p to the ground state 1s 2s 2p 3s is accompanied by the emission of yeiiow iight at 589 nm. Excited states of an atom are needed to describe its spectrum. 

The major Chi a/b-protein 2 and minor Chi a/b-protein 1 were isolated from barley (Hordeum vulgare L. cv Bonus) free from contamination by other Chl-proteins using sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis (Machold et al. 1979). FDMR at 4.2 K was performed as previously described (Searle et al. 1981) except that the 476 nm line of a Coherent Radiation CR3 Ar" " (CW) laser was used to excite Chi b specifically. The same set-up (detailed in Searle et al., to be published) was used to measure front-surface fluorescence excitation and emission spectra, and also to carry out the fluorescence fading measurements (Avarmaa 1977), all at 4.2 K. Chi fluorescence decay kinetics and fluorescence emission spectra at 293 K were measured using excitation from a mode-locked Coherent Radiation CR18 Ar+ laser (100 ps FWHM pulses with < 10 photons cm 2 pulse" ), the pulse train being modulated at 330 kHz. 

Absorption of a photon is accompanied by the excitation of an electron from a lower-energy atomic orbital to an orbital of higher energy. Not all possible transitions between atomic orbitals are allowed. For sodium the only allowed transitions are those in which there is a change of +1 in the orbital quantum number ) thus transitions from s—orbitals are allowed, but transitions from s d orbitals are forbidden. The wavelengths of electromagnetic radiation that must be absorbed to cause several allowed transitions are shown in Figure 10.18. 

Figure 9.42 Intensity of sodium atom fluorescence as a function of time following excitation of Nal to the V potential with a pump wavelength of 307 nm (pulse duration ca 50 fs) and a probe wavelength of (a) 575 nm, (b) 580 nm, (c) 589 nm, and (d) 615 nm. (Reproduced, with permission, from Rose, T. S., Rosker, M. J. and Zewail, A. H., J. Chem. Phys., 91, 7415, 1989)...

Intense sodium D-line emission results from excited sodium atoms produced in a highly exothermic step (175). Many gas-phase reactions of the alkafl metals are chemiluminescent, in part because their low ioni2ation potentials favor electron transfer to produce intermediate charge-transfer complexes such as [Ck Na 2] (1 )- There appears to be an analogy with solution-phase electron-transfer chemiluminescence in such reactions. 

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