Gallane at Last

Gallane condenses at low temperatures as a white solid that melts at ca. 223 K to form a colorless, viscous liquid. The rate of vaporization of the solid at 210 K is consistent with a vapor pressure on the order of 1 mm Hg. Samples of the material in the condensed phase (liquid or solution) decompose to the elements at temperatures in excess of 243 K. At a pressure of 10 mm Hg the vapor has a half-life of about 2 min at ambient temperatures. 

Qualitative and quantitative analysis for chlorine confirms, moreover, that the compound can be made free from contamination by chlorogal-lanes. 

Very different infrared spectra are exhibited by the vapor or by solid matrices formed by codepositing the vapor with an excess of a suitable inert gas at ca. 20 K (see Fig. 6). Here the pattern and energies of the absorptions, and particularly the rotational structure of individual absorptions of the vapor, testify to the presence of a relatively simple molecule with a momental ellipsoid in which at least one of the principal moments of inertia is unusually small for a gallium derivative. Three aspects of the spectra turn out to be critical to the unambiguous identification of the gaseous molecule. 

Dimensions of Some Gaseous Gallium Hydrides as Determined by Electron Diffraction0 

Observed and Calculated Vibrational Properties of the Ga2H6 and Ga2D6 Molecules (56,105,109)° 

Hi) Most of the bands in the infrared spectrum of gallane vapor carry unmistakable signs of rotational structure no better example is provided than that of the two absorptions near 1980 cm the appearance of which, as measured at moderately high resolution with the aid of a multiple reflection cell, is illustrated in Fig. 5. There are, it appears, two types of band. One type, exemplified by the band at 1976 cm S displays all the features characteristic of a parallel band of a highly prolate symmetric top molecule (see Section III.B.l). The other type has the attributes of a perpendicular band of such a molecule (as witness the band at 1993 cm in Fig. 5). 

HU) In the pattern and wave numbers of the vibrational transitions observed in infrared absorption, there is no change of consequence when the vapor species are trapped in a solid inert matrix at low 

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The experiments described in the preceding sections leave little room for doubt that the base-free trihydride of gallium has at last been run to earth. It can be prepared in amounts up to 500 mg. While decomposing to the elements at ambient temperatures, gallane vaporizes at low... 

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