Gashyphen;phase average structures for the groundhyphen;vibrational statelpar;rzrpar;for ethane and diborane have been determined by a critical comparison of the experimental results obtained from electron diffraction (average internuclear distancesrg) and those obtained from highhyphen;resolution infrared and Raman spectroscopy (rotational constantsBzlpar;agr;rpar;). Experimental values have been taken from the recent literature and converted into the average structurelpar;rzorragr;0rpar;. Thergandragr;0distances determined from electron diffraction carry uncertainties less than those in therzdistances determined from rotational constants, because the latter structures are very sensitive to assumptions about the unknown isotope differences in the structures. On the other hand, the average moments of inertia from spectroscopy are much more precise than those calculated from diffraction internuclear distances. Examinations of the data have led to the followingrzstructures with standard errors: For C2H6,rzlpar;Csngbnd;Hrpar;thinsp;equals;thinsp;1.0957thinsp;plusmn;thinsp;0.002 Aring;, rzlpar;Csngbnd;Crpar;thinsp;equals;thinsp;1.5319thinsp;plusmn;thinsp;0.002 Aring;,andang;Csngbnd;Csngbnd;Hthinsp;equals;thinsp;111.5deg;thinsp;plusmn;thinsp;0.3deg;; for C2D6,rzlpar;Csngbnd;Drpar;thinsp;equals;thinsp;1.0941thinsp;plusmn;thinsp;0.002 Aring;, rzlpar;Csngbnd;Crpar;thinsp;equals;thinsp;1.5300thinsp;plusmn;thinsp;0.002 Aring;,andang;Csngbnd;Csngbnd;Dthinsp;equals;thinsp;111.4deg;thinsp;plusmn;thinsp;0.3deg;; and for B2H6,rzlpar;Bsngbnd;Htrpar;thinsp;equals;thinsp;1.192thinsp;plusmn;thinsp;0.01 Aring;, rzlpar;Bsngbnd;Hbrpar;thinsp;equals;thinsp;1.329thinsp;plusmn;thinsp;0.005 Aring;, rzlpar;Bsngbnd;Brpar;thinsp;equals;thinsp;1.770thinsp;plusmn;thinsp;0.005 Aring;,ang;Htsngbnd;Bsngbnd;Htthinsp;equals;thinsp;121.8deg;thinsp;plusmn;thinsp;3deg;,andang;Hbsngbnd;Bsngbnd;Hbthinsp;equals;thinsp;96.5deg;thinsp;plusmn;thinsp;0.5deg;. It was possible to increase the resolving power of the diffraction analysis of diborane by inclusion of calculated Bsngbnd;H mean amplitudes.The effective complementary use of electronhyphen;diffraction and spectroscopic data for determining reliable gashyphen;phase structures and the relative merits of the two alternative representations of theaverage structurelpar;rgandrzrpar;have been discussed.
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