Alkali metal dimers

Selective Photolysis and Photoionization of Alkali Metal Dimers... 

This is a severe drawback in the case of equilibrium studies of metal molecules since, as a rule, such molecules are minor vapor components and maximum sensitivity is required for their thermodynamic evaluation. However, very precise ionization potentials can be measured using photoionization spectroscopy (5,28). Berkowltz (28) reviewed early work concerning alkali metal dimers. Herrmann et al. ( ) have measured the ionization potentials of numerous sodium, potassium and mixed sodium-potassium clusters. For most of these clusters the atomization energies of the neutral molecules are not known. Therefore, the dissociation energies of the corresponding positive ions cannot be calculated. 

These reactions were pioneered by Grice and co-workers who first addressed the reactivity of alkali metal dimers with halogen molecules [108-111]. These reactions are four-center harpoon reactions. They are interesting because of the possibility of two sequential electron jumps [112. ... 

Chemiluminescent channels have also been observed in this type of reaction [113]. Reactions of alkali metal dimers with oxygen molecules have also been reported [114-116],... 

The polyatomic species Li4, Naj, Cuj, Agj, and Auj were detected for the first time by Knudsen effusion mass spectrometry, and their enthalpies of dissociation were determined [80, 127, 180]. The study of the molecule Li by Wu [180] complements his earlier investigation of Lij and Lij [223]. The binding energies of alkali metal dimers and polymers obtained by different... 

The reactions of alkali-metal dimers have been investigated, but to the authors knowledge the reactions of mixed dimers have not been studied, e.g. NaK, and any effects due to altering the reaction partner investigated. 

Struve et al. [81] have measured the sodium D line chemiluminescence produced in the reaction of Na2 and Cl atoms. Evans and Polanyi [264] suggested two possible mechanisms for the chemiluminescence, namely the direct reaction of alkali-metal dimer with a halogen atom to produce electronically excited sodium Na2 + Cl NaCl + Na(3 P)... 

Dissociation and predissociation of alkali-metal dimers in one- and two-photon s absorption processes have been investigated experimentally S S S and theoretically. S The fluorescence from Na( P ) atoms formed in the dissociation of Na2 via excitation of the - transitions... 

A brief report has appeared on the crossed-beam reaction between Ba and LiCl, using laser-induced fluorescence detection of the BaCl product, which gives a lower bound for the bond-dissociation energy of BaCl of 110 3 kcal mol-1.242 Similar studies on the reactions of alkali-metal dimers with hydrogen atoms and molecules 243 and the photodissociation of alkali-metal iodides244 have been reported. 

Chemiluminescence and photoluminescence in diatomic iron oxide, Rb2, and alkali-metal dimers with halogen atoms and metal vapour-oxidant flames,202 203 lifetime measurements of selectively excited states of diatomic hydrides,204 photodissociation of alkali-metal halide vapours,206 spin-orbit relaxation of the HTe ( 2IIi) radical,20 the photodecomposition of metal carbonyl anions such as [Mn(C04)] in the vapour phase,207 and the fluorescence of Rhodamine 6G in the vapour phase 208 have been studied in recent reports. In the last study it was concluded that an insufficient concentration of the fluorescing dye could be maintained in the vapour phase to permit laser action to occur. 

Relaxation of Vibrationally Excited Alkali Metal Dimers 104... 

Photoassociation experiments involving alkali-metal systems have stimulated considerable interest in chemical reactivity in alkali-metal dimer-alkali-metal atom collisions at ultracold temperatures [14]. Rearrangement collisions in identical particle alkali-metal trimer systems occur without energy barrier, and recent studies have... 

Reactions of Heteronuclear and Isotopically Substituted Alkali-Metal Dimer Systems... 

Reactive collisions involving heteronuclear molecules are currently of great interest. A major goal of recent experiments has been to produce heteronuclear alkali-metal dimers in their electronic ground state. Examples include RbCs [111,118,119], NaCs [120,121], KRb [122,123], LiCs [124], and mixed isotopes Li Li [125]. Quantum dynamics calculations for heteronuclear systems are more difficult. They are more interesting from a chemistry perspective because the reactive channels in collisions of heteronuclear molecules can be distinguished from inelastic channels. 

Cvitas, M.T., Sold i, R, Hutson, J.M., Honvault, R, and Launay, J.-M., Ultracold collisions involving heteronuclear alkali metal dimers, Phys. Rev. Lett., 94,200402,2005. 

Historically, the first method for enhancing one-photon PA so that lower-u, more deeply bound vibrational levels could be directly produced was the use of upper-state potential energy curves having two minima with an intervening barrier [107, 122]. Such double-minimum potentials are well known in the alkali metal dimers (e.g., [123-125]). The 0 state of Cs2 has been studied in some detail because the production of molecules in more deeply bound levels is favored [126,127]. Other promising double-minimum states have been proposed for study [40,128]. Of particular significance in each case is the energy and intemuclear distance at which... 

Figger and co-workers [11] observed chemiluminescence in their crossed-beam experiment of alkali metal dimers with oxygen molecules. In the reactions of Cs2, Rb2, K2 and Li2, D-line emission as well as continuous chemiluminescence from the collision zone were recorded. They attributed this emission to the formation of electronically excited products from the reactions M2 + O2 MO2 + M and M2 + O2 —> MO2 + M. No emission was observed for the Na2 reactions due to their lower exothermicities. 

Bond order can be misleading, however. If we apply a Lewis structure model to Na2, we would assign it a bond order of 1, the same as CI2, and therefore might expect it to have a similar force constant. However, the alkali metal dimers form bonds primarily with weakly bound single valence electrons. The resulting... 

Cyclopentadienyltitanium trichloride associated with amalgams or alkali metals dimerizes ethylene to 1-butene [93]. 

The reactions of alkali metal dimers with X2 and RX are quite interesting because of the many reaction paths including chemiluminescence and chemi-ionization/ Based upon measurement of the alkali halide product, the angular distributions show a peak in the forward direction, as well as some scattering in the backward direction. In most cases three products, M + MX + X (or R), are probably formed. The potential surfaces for these systems must involve some deep wells and, as data become available, the energy disposal for this class of reaction should be most interesting. 

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