| Popis: |
A previous electron-spin resonance (ESR) study of HC${\mathrm{N}}^{\ensuremath{-}}$ in KCl at 77\ifmmode^\circ\else\textdegree\fi{}K yielded an isotropic spectrum indicating rapid tumbling of the radical. At 4.2\ifmmode^\circ\else\textdegree\fi{}K this tumbling is frozen out and ESR spectra recorded at this temperature are anisotropic, permitting a complete determination of the magnetic parameters of HC${\mathrm{N}}^{\ensuremath{-}}$. The experimental results show that the planar radicals lie in {110} crystal planes with the CN bonds parallel to $〈110〉$ crystal axes. The components of the electronic $g$-factor tensor, the proton hyperfine-splitting (hfs) tensor, and nitrogen hfs tensor are as follows: ${g}_{1}=2.0023$, ${g}_{2}=2.0005$, and ${g}_{3}=2.0035$; ${{A}_{1}}^{(\mathrm{H})}=136.5$, ${{A}_{2}}^{(\mathrm{H})}=141.3$, and ${{A}_{3}}^{(\mathrm{H})}=131.3$ Oe; and ${{A}_{1}}^{(\mathrm{N})}=20.9$ and ${{A}_{2}}^{(\mathrm{N})}={{A}_{3}}^{(\mathrm{N})}=0.0$ Oe. Axis 1 lies in the molecular plane and is perpendicular to the CN bond, axis 2 is parallel to the CN bond, and axis 3 is perpendicular to the molecular plane. The carbon-13 hfs tensor has the components: ${{A}_{{1}^{\ensuremath{'}}}}^{(\mathrm{C})}=90.0$, ${{A}_{{2}^{\ensuremath{'}}}}^{(\mathrm{C})}=65.6$, and ${{A}_{3}}^{(\mathrm{C})}=68.6$ Oe, where axes 1\ensuremath{'} and 2\ensuremath{'} lie in the molecular plane and make angles of 34\ifmmode^\circ\else\textdegree\fi{} with axes 1 and 2, respectively. From these results we deduce an approximate value of 131\ifmmode^\circ\else\textdegree\fi{} for the HCN bond angle and the following values for the unpaired electron density on the hydrogen, nitrogen, and carbon atoms: ${\ensuremath{\rho}}_{\mathrm{H}}=0.27$, ${\ensuremath{\rho}}_{\mathrm{C}}=0.32$ and ${\ensuremath{\rho}}_{\mathrm{N}}=0.41$. |
