Uranium Monosulfide. III. Thermochemistry, Partial Pressures, and Dissociation Energies of US and US2

摘要

A masshyphen;spectrometric study of the sublimation of uranium monosulfide has been performed over the temperature range 1825deg; to 2400deg;K. The data are combined with the previous measurements of absolute rate of effusion by means of a new method of calculation which effects an absolute pressure calibration of the spectrometer and allows a determination of the partial pressures of U, US, and US2in the vapor, the enthalpies and entropies of sublimation to atoms and molecules, and the dissociation energies of US and US2. The partial pressures of U, US, and US2at 2020deg;K are in the ratios 1/0.27/0.001. The data for the several sublimation processes are as follows:thinsp;thinsp;thinsp;thinsp;Reactionthinsp;thinsp;thinsp;thinsp;thinsp;thinsp;thinsp;thinsp;thinsp;thinsp;thinsp;thinsp;thinsp;thinsp;thinsp;thinsp;thinsp;thinsp;logPthinsp;lpar;atmrpar;Dgr;Hcompfn;2020thinsp;kcalsol;moleDgr;Scompfn;2020thinsp;calsol;molemiddot;degUSlpar;srpar;equals;USlpar;grpar;logPUSequals;lpar;7.606plusmn;0.091rpar;minus;lpar;31thinsp;030plusmn;190rpar;sol;T142.0plusmn;0.934.8plusmn;0.4USlpar;srpar;equals;Ulpar;grpar;plus;Slpar;grpar;logPUequals;lpar;7.323plusmn;0.081rpar;minus;lpar;29thinsp;600plusmn;170rpar;sol;T270.9plusmn;0.1665.0plusmn;0.72USlpar;srpar;equals;US2lpar;grpar;plus;Ulpar;grpar;logPUS2equals;lpar;6.36plusmn;0.26rpar;minus;lpar;33thinsp;430plusmn;580rpar;sol;T288.4plusmn;3.762.6plusmn;1.2The quoted uncertainties are standard deviations. The dissociation energies for US and US2and the estimated uncertainties areD0lpar;USrpar;equals;133.8plusmn;2.3thinsp;kcalsol;mole orthinsp;5.80plusmn;0.10thinsp;eV,D0lpar;US2rpar;equals;252plusmn;4thinsp;kcalsol;mole orthinsp;10.9plusmn;0.2thinsp;eV.