Determination of consecutive bond energies by photoionization of SbHn(n=1ndash;3)

摘要

A photoionization mass spectrometric study of SbH3is presented. The adiabatic ionization potential (IP) of SbH3is le;9.40plusmn;0.02 eV. The lowest energy fragment ion, SbH+(+H2), has an appearance potential (0 K) of 9.730plusmn;0.008eV, while SbH2+has an AP of 11.66plusmn;0.02 eV. The transient species SbH2and SbH are generatedinsituby reacting F atoms with SbH3. The IP of SbH2, forming SbH2+(Xthinsp;1A1), is 8.731plusmn;0.012 eV. The IP of SbH (Xthinsp;3Sgr;minus;,0+) to form SbH+(Xthinsp;2Pgr;1/2) is probably 8.753plusmn;0.009 eV, but certainly 8.79 eV. Autoionizing structure in the photoion yield curve of SbH+(SbH) is interpreted as Rydberg series converging to SbH+(athinsp;4Sgr;minus;), which appears to be split into 1/2 and 3/2 components, with IPrsquo;s of 10.843plusmn;0.011 eV and 10.866plusmn;0.011 eV. The difference in IPrsquo;s (Sbndash;SbH, SbHndash;SbH2) appears to conform to the extended Goddardndash;Harding model, when adjusted for spinndash;orbit splittings. The derived heats of formation are Dgr;Hf00(SbH)=59.1plusmn;0.3 kcal/mol and Dgr;Hf00(SbH2)=52.5plusmn;0.6 kcal/mol. These values lead toD0(SbH)=56.4plusmn;1.0,D0(HSbndash;H)=58.3plusmn;0.6,D0(H2Sbndash;H)=67.5plusmn;0.5 (in kcal/mol). The differences in successive bond energies, 1.9plusmn;1.2 and 9.2plusmn;0.8 kcal/mol, depart significantly from the constant value (4.44 kcal/mol) predicted by the Goddardndash;Harding model. A rationalization is presented, that incorporates relativistic effects. This relativistic picture implies that for BiHn,D0(BiH)gsim;D0(HBindash;H), a conclusion for which some experimental evidence exists. However, relativisticabinitiocalculations, which agree rather well in their calculated differences in successive bond energies for SbHn, do not predict this reversal in BiHn.