Hydride alkali

Acetylene Bromine, chlorine, brass, copper and copper salts, fluorine, mercury and mercury salts, nitric acid, silver and silver salts, alkali hydrides, potassium metal... 

The compound sodium hydride, formed in reaction (29), is a crystalline compound with physical properties similar to those of sodium chloride. The chemical properties are very different, however. Whereas sodium burns readily in chlorine, it reacts with hydrogen only on heating to about 300°C. While sodium chloride is a stable substance that dissolves in water to form Na+(aqJ and CV(aq), the alkali hydrides bum in air and some of them ignite spontaneously. In contact with water, a vigorous reaction occurs, releasing hydrogen ... 

The key to the attachment of the donor to the polymer lies in the preparation of suitably monofunctionalized donors. A variety of synthetic procedures have been employed and are outlined in Table II. Conversion of the functionalized alkali salt derivatives were accomplished by reaction with the alkali hydroxide (CsOH or KOH in alcohol) or by reaction with an alkali hydride (i.e. KH in tetrahydrofuran). The latter reaction was found to proceed more cleanly and conveniently. 

Heating the adduct of ethylene oxide and sulfur dioxide with primary alcohols in the presence of alkali hydrides or a transition-metal halide yields dialkyl sulfites (107). Another method for the preparation of methyl alkyl sulfites consists of the reaction of diazomethane with alcoholic solutions of sulfur dioxide (108). 

LiH+Hg=LiHg+iH2. The hydrides are strong reducing agents—the oxides of lead, copper, etc., are reduced to the metallic state. Lithium hydride slowly decomposes absolute alcohol, forming the alcoholate and hydrogen the hydrated alcohol is vigorously decomposed. The alkali hydrides are insoluble in ether and benzene. 

The occurrence of transition and rare earth metal hydrides is shown in Figure 1. Not shown are the alkali hydrides and alkaline earth dihydrides that bear a close resemblence to their halide counterparts. Also not shown are compounds formed from elements to the right that are the topic of much of the rest of this symposium volume. 

Table 3-3.—Bond-Energy Values for Alkali Hydride Molecules...

Various reducing agents have been used for the generation of selenolates from diselenides or selenocyanates. Alkali metals M (M = Li, Na, K)149,150 or alkali hydrides MH (M = Li, Na, K)151,152 can generate the corresponding selenolate anions such as 80 these are more reactive than the borane complexes of type 77 (Scheme 15). Diaryl diselenides are easier reduced than dialkyl diselenides, but the mechanism for the reduction of selenocyanates is complex and can lead to either diselenides or selenolates.153,154... 

PsH 1968 2.35 11)<°) Extrapolation to zero density for a sequence of alkali hydride crystals [69]. 

The recently available spectroscopic data and the RKR potentials of the alkali hydrides allow us to determine the "experimental" values of the parameters relevant to the transition probability of the charge transfer processes. In the Landau-Zener model these parameters are the energy gap between the and X S adiabatic potentials at the avoided crossing distance and the coupling matrix elements. In this paper the coupling matrix elements are evaluated in a two-state ionic-covalent interaction model. The systema-tic trends found in the alkali hydride series for their X e potentials are presented. This leads to a simple model for the ionic potentials. 

Table I. Parameters obtained from the optical spectra of the alkali hydrides.

When we plot the energy of the X state potential minimum relative to the energy of the ion pairs as a function of R the inverse of the internuclear distance at the minimum, we get a straight line correlation among the alkali hydrides (see Figure 1) ... 

Figure 1. Correlation between the energy of the potential minima relative to the ion pair dissociation limit and the reciprocal of the equilibrium bond distance for the X X state alkali hydrides.

Figure 4 shows the known RKR turning points for both the X and A states of the alkali hydrides. The internuclear distance is scaled by the equilibrium bond distance in the state. 

Figure 4. RKR turning points of the and states of the alkali hydrides plotted vs. the reduced internuclear distance R/Re. Key see Fig. 3.

The systematics found in the alkali hydride potentials suggest that it might be possible to model a simple ionic potential to reflect the behavior of the whole series of alkali hydrides. Here we construct a "practical" diabatic curve which reflects the physical properties, e.g. the dipole moment function.. We expect our diabatic curve to follow the ionic part of the adiabatic potential and to begin to deviate in the avoided crossing region. 

The parameters A and p are determined by a nonlinear least square fit of equation (1) to the RKR inner turning points of each of the alkali hydrides. This fitting procedure is justified by the fact that the magnitude of the dipole moment functions of LiH (25, 26) and NaH (33) at these internuclear distances are very close to those of opposite point charges a distance R apart. 

Finally we note that similar scaling procedures to that shown here for the alkali hydrides are discussed extensively for the alkali dimers in this volume (43). 

New spectroscopic measurements of the alkali hydrides have provided information related to the dynamical charge transfer process for these systems. We have examined the RKR potentials derived from these spectra. Several striking regularities for the X l potentials are presented along with an interpretation based on a simple model of ionic potentials for internuclear distances shorter than the crossing distance R. . 

In this study we used the scaled theoretical potential curves of Olson and Liu (21), Stevens, Karo and Hiskes ( ), and Laskowski and Stall cop (2T) to make a short extrapolation of the X E" RKR potentials into the avoided crossing region. Experimental measurements to obtain strictly experimental RKR potentials for this region are in progress. New optical measurements on the dipole moments (, ), the transition moments (38> nd radiative lifetimes (, ) of the alkali hydrides are also becoming available. This type of information will soon provide additional details about the ionic-covalent interactions in these molecules. 

Several attempts have been made during the last few years to study the formation of alkali hydrides in the vapor phase when a mixture of alkali metal vapor and hydrogen is exposed to laser irradiation which photoexcites the alkali atom. The present work is devoted to the following overall reactions ... 

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