Protactinium monoxide

Unlike uranium pentaehloride, which is thermally unstable, protactinium pentachloride sublimes unchanged above 180°C in vacuo. It is a yellow, moisture-sensitive solid which is slightly soluble in benzene, tetrahydrofuran, and carbon tetrachloride. Visible absorption speetra have been reeorded for solutions in the last two solvents and in aleohol (110). Reactions with hydrogen, aluminum, oxygen, and silicon tetra-iodide are discussed below. It is unaffected by carbon monoxide at 350°C in a sealed tube. 

Oxide films form readily on protactinium metal and the monoxide PaO has been identified (125) by X-ray powder diffraction. It is cubic, like other actinide monoxides, with = 4.961 A and slowly oxidizes to PaO 2. 

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