MoleculargValues, Magnetic Susceptibility Anisotropies, Diamagnetic and Paramagnetic Susceptibilities, Second Moment of the Charge Distribution, and Molecular Quadrupole Moments of H3CCN and H3CNC

摘要

The highhyphen;field, linear and quadratic Zeeman effect has been observed in methyl cyanide (H3CCN) and methyl isocyanide (H3CNC). Both spectra are complicated by the presence of the14N nuclear quadrupole coupling. The H3CNC system leads to uncoupled spectra in high fields, and the H3CCN system does not exhibit fully uncoupled spectra even at fields of 25 000ndash;30 000 G. In the numbers given below,cthinsp;equals;thinsp;bis perpendicular to theC3oraaxis. The perpendiculargvalues in H3CC14N and D3CC14N aregperp;thinsp;equals;thinsp;minus;thinsp;0.0338thinsp;plusmn;thinsp;0.0008andgperp;thinsp;equals;thinsp;minus;thinsp;0.0315thinsp;plusmn;thinsp;0.0008, respectively. The sign of the electric dipole moment is plus;H3CCNsngbnd;. The average magnetic susceptibility anisotropy from the above isotopic molecules iskhgr;perp;thinsp;minus;thinsp;khgr;Verbar;thinsp;equals;thinsp;lpar;10.2thinsp;plusmn;thinsp;1.0rpar;thinsp;times;thinsp;10minus;6ergsol;G2middot;mole. AssuminggVerbar;thinsp;equals;thinsp;0.310from other similar systems gives the molecular quadrupole moment ofQVerbar;thinsp;equals;thinsp;minus;lpar;1.8thinsp;plusmn;thinsp;1.2rpar;thinsp;times;thinsp;10minus;26esumiddot;cm2. Using the known molecular structure and abovegvalues allows a determination of the paramagnetic susceptibilities which arekhgr;perp;pthinsp;equals;thinsp;lpar;145.3thinsp;plusmn;thinsp;1.0rpar;thinsp;times;thinsp;10minus;6ergsol;G2middot;moleandkhgr;Verbar;pthinsp;equals;thinsp;lpar;9.6thinsp;plusmn;thinsp;0.5rpar;thinsp;times;thinsp;10minus;6ergsol;G2middot;mole. Combining the above experimental magnetic susceptibility anisotropy with the known bulk magnetic susceptibility gives the total and diamagnetic terms,khgr;perp;thinsp;equals;thinsp;minus;lpar;24.1thinsp;plusmn;thinsp;0.4rpar;, khgr;perp;dthinsp;equals;thinsp;minus;lpar;169.4thinsp;plusmn;thinsp;1.1rpar;, khgr;Verbar;thinsp;equals;thinsp;minus;lpar;34.6thinsp;plusmn;thinsp;0.5rpar;, andkhgr;Verbar;dthinsp;equals;thinsp;minus;lpar;44.2thinsp;plusmn;thinsp;1.0rpar;, all in units of 10minus;6erg/G2middot;mole. The individual elements in the tensor describing the second moment of the electronic charge distribution arelang;c2rang;thinsp;equals;thinsp;5.2thinsp;plusmn;thinsp;0.3andlang;a2rang;thinsp;equals;thinsp;34.7thinsp;plusmn;thinsp;0.4in units of 10minus;16cm2. The Zeeman spectra of H3CC15N was also observed to confirm the above results with the14N isotope. The moleculargvalue in H3CC15N isgperp;thinsp;equals;thinsp;minus;thinsp;0.0317thinsp;plusmn;thinsp;0.0003andlpar;khgr;perp;thinsp;minus;thinsp;khgr;Verbar;rpar;thinsp;equals;thinsp;lpar;10.5thinsp;plusmn;thinsp;0.5rpar;thinsp;times;thinsp;10minus;6ergsol;G2middot;mole. The perpendiculargvalue and magnetic susceptibility anisotropy of H3C14NC aregperp;thinsp;equals;thinsp;minus;thinsp;0.0546thinsp;plusmn;thinsp;0.0015andkhgr;perp;thinsp;minus;thinsp;khgr;Verbar;thinsp;equals;thinsp;lpar;13.5thinsp;plusmn;thinsp;0.7rpar;thinsp;times;thinsp;10minus;6ergsol;G2middot;mole. The sign ofgperp;was not determined experimentally; however, an analysis of the molecular quadrupole moment indicates the proper choice of sign. AssuminggVerbar;thinsp;equals;thinsp;0.310from similar systems gives the molecular quadrupole moment ofQVerbar;thinsp;equals;thinsp;minus;lpar;2.7thinsp;plusmn;thinsp;1.6rpar;thinsp;times;thinsp;10minus;26esumiddot;cm2. Using techniques as outlined above give the paramagnetic susceptibilities ofkhgr;perp;pthinsp;equals;thinsp;137.8thinsp;plusmn;thinsp;0.9andkhgr;Verbar;pthinsp;equals;thinsp;9.6thinsp;plusmn;thinsp;0.6in units of 10minus;6erg/G2middot;mole. The total and diamagnetic susceptibilities are also estimated. The anisotropy in the second moment of the electronic charge distribution islang;a2rang;thinsp;minus;thinsp;lang;c2rang;thinsp;equals;thinsp;lpar;27.0thinsp;plusmn;thinsp;0.5rpar;thinsp;times;thinsp;10minus;16cm2.