Sodium dimers

In Reference [38], it is further shown that suppression of the spontaneous emission can be equally well achieved in a molecular system. The difficulty with molecular systems lies in the fact that there is usually a multitude of final states to which the system can emit. In this example, suppressing the emission from a particular vibrational state a) belonging to the 1 S (A) electronic manifold of the Sodium dimer is considered, when aided by a particular vibrational state b) belonging to the 2 electronic manifold. The relevant potentials are displayed in Figure 9.12. 

Figure 9.13 Suppression of the spontaneous emission of the sodium dimer. The optimization time T (marked by a triangle) is 0.2/r(= 10 ns), and the total time range displayed is up to 3/F(= 150 ns). AE is the Autler-Townes splitting induced by die CW laser and F is the natural linewidth. Reprinted figure by permission from Ref. [38]. Copyright 2003 by the American Physical Society.

There are many systems of different complexity ranging from diatomics to biomolecules (the sodium dimer, oxazine dye molecules, the reaction center of purple bacteria, the photoactive yellow protein, etc.) for which coherent oscillatory responses have been observed in the time and frequency gated (TFG) spontaneous emission (SE) spectra (see, e.g., [1] and references therein). In most cases, these oscillations are characterized by a single well-defined vibrational frequency, It is therefore logical to anticipate that a single optically active mode is responsible for these features, so that the description in terms of few-electronic-states-single-vibrational-mode system Hamiltonian may be appropriate. 

Na2 (2) the possibility of controlled "hot band" formation through disruption of the free jet expansion allowing the mapping of vlbronic structure in the ground electronic state of sodium trimer, and (3) the observation of very efficient energy transfer between sodium dimer and polyatomic sodium. The current studies are discussed in the light of recent experimental and theoretical characterization of Nas. Preliminary studies of the reaction Nas + Cl - NaCl + Na2 are discussed as they pertain. to the dissociation energy of Naa. 

The solvent-free phenyl derivatives of the heavier alkali metals have not been structurally characterized. Phenyl sodium dimers crystallize in the presence of donors such as, PMDTA and TMEDA. Using the bulky mesityl-substituted derivatives, a solvent-free arylsodium compound has been characterized [Na(C6H3Mes2-2,6)]2. ... 

The amounts of sodium over mixtures of cryolite and aluminum have been measured by Ono et al. (8), Dewing (9), and by Stokes and Frank (10). The data have been corrected for the formation of sodium dimer by using JANAP functions for Nag(g) and Na(g) to determine the equilibrium constants for the reaction Nag(g) 2 Na(g). Our evaluation of this data is presented below. We were unable to evaluate the data of Stokes and Prank (1 ) due to lack of appropriate data on the activities of NagAlPg(t). Also shown in the table are the emf work of Dewing (IJJ, and the equilibrium study of Mashovets and Yudin (12). 

INVESTIGATION OF AUTLER-TOWNES EFFECT IN SODIUM DIMERS... 

Investigation of Autler-Townes effect in sodium dimers... 

This represents a formidable practical problem, as one is very unlikely to find isolated atoms with two nonorthogonal dipole moments and quantum states close in energy. Consider, for example, a V-type atom with the upper states 11), 3) and the ground state 2). The evaluation of the dipole matrix elements produces the following selection rules in terms of the angular momentum quantum numbers J — J2 = 1,0, J3 — J2 = 1,0, and Mi — M2 = M3 — M2 = 1,0. Since Mi / M3, in many atomic systems, p12 is perpendicular to p32 and the atomic transitions are independent. Xia et al. [62] have found transitions with parallel and antiparallel dipole moments in sodium molecules (dimers) and have demonstrated experimentally the effect of quantum interference on the fluorescence intensity. We discuss the experiment in more details in the next section. Here, we point out that the transitions with parallel and antiparallel dipole moments in the sodium dimers result from a mixing of the molecular states due to the spin-orbit coupling. 

The energy-level scheme of the molecular system considered in the experiment is shown in Fig. 20. The five-level molecule consists of two upper levels <7j) and a2), two intermediate levels b) and d), and a single ground level c). The upper levels are separated by the frequency 0012, which is much smaller than the frequencies a>u, and 002b of the a ) —> b) and 2) —> b) transitions and the frequencies o>id and (d2d of the a ) —> d) and ci2) —> d) transitions. As in the sodium dimers used in the experiment, we assume that the frequencies Oj and 0)26 correspond to the visible region, while the frequencies ou and 0)2d... 

The 14 electronic states of the sodium dimer which are considered are shown in Fig. 25 (left panel). A selection of transition dipole moments are displayed in the right panel for illustration. Note, however, that all transition dipole moments... 

An alternative approach to trace analyte detection results from the measurement of chemiluminescence in a laser-generated plume of plasma, formed when the laser beam evaporates a small amount of sample (43). In these experiments, a pulsed excimer laser-induced-plasma, formed by laser vaporization and ionization, is probed direcdy to measure ion intensity. Ground state sodium atoms, excited state copper atoms, and sodium dimer molecules have all been monitored using this technique. This laser enhanced ionization may well be one of a very few techniques which can be used to probe extremely dense plasmas with good spatial and temporal resolution. 

Ahrashkevich, D.G., Averhukh, l.S., and Shapiro, M., Optimal squeezing of vibrational wave packets in sodium dimers, J. Chem. Phys., 101, 9295,1994. 

For the neutral sodium dimer and trimer, beautifully resolved optical spectra are available, which are in excellent agreement with quantum-chemistry-type calculations [10, 11]. The early experiments on larger neutral clusters [12] gave many beautiful results but had one serious drawback. At best it is very difficult to mass-select neutral clusters, so that one has nearly always to work with a broad distribution of masses. In some cases it was possible, nevertheless, to deduce optical data [5, 12]. 

This paper presents our results from crossed-beam studies of the reactions of sodium dimers with oxygen molecules. For this seemingly simple chemical system, there are at least four distinct reaction pathways that were energetically accessible under our experimental conditions ... 

Since then the ultrafast dynamics of a few molecular, especially dimer, systems have been studied. Zewail observed the vibrational and rotational revival of excited I2 [21-23]. Stolow studied the same system, applying femtosecond pump probe zero-kinetic-energy (ZEKE) photoelectron spectroscopy [24, 25]. Gerber observed fascinating features in the ultrafast dynamics of the sodium dimer s multiphoton ionization (MPI) (see Fig. 1.1a), induced... 

Spectroscopic Basics. The sodium dimer s first singlet electronic state A 17+ has been studied by different cw techniques using laser-induced fluorescence, optical-optical double resonance, and Fourier transform spectroscopy [319, 320, 330-332]. Ro-vibrational levels could be numbered and... 

A promising candidate might be the solvated sodium dimer excited to its double-minimum state. Employing a pump and control scheme, as shown in Fig. 6.1, will enable the transfer of the initially covalent bond-length isomer, to its ionic isomer which should favor the... 

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