Microwave Spectra and Molecular Structures of Methyl Cyanide and Methyl Isocyanide

Certain of the pure rotational lines of methyl cyanide and methyl isocyanide have been measured and the following molecular properties have been obtained. The moments of inertia, $I_B$, × ${10}^{-4\mathrm{}}$ g ${\mathrm{cm}}^2$, are: for ${\mathrm{C}}^{12}$ ${\mathrm{H}}_3$ ${\mathrm{C}}^{12}$ ${\mathrm{N}}^{14}$, ${91.20}_{34}$; for ${\mathrm{C}}^{12}$ ${\mathrm{H}}_3$ ${\mathrm{C}}^{13}$ ${\mathrm{N}}^{14}$, ${91.24}_{86}$; for ${\mathrm{C}}^{12}$ ${\mathrm{D}}_3$ ${\mathrm{C}}^{12}$ ${\mathrm{N}}^{14}$, ${106.76}_{66}$; for ${\mathrm{C}}^{12}$ ${\mathrm{D}}_3$ ${\mathrm{C}}^{13}$ ${\mathrm{N}}^{14}$, ${106.89}_{48}$; for ${\mathrm{C}}^{12}$ ${\mathrm{H}}_3$ ${\mathrm{N}}^{14}$ ${\mathrm{C}}^{12}$, ${83.45}_{50}$; for ${\mathrm{C}}^{12}$ ${\mathrm{H}}_3$ ${\mathrm{N}}^{14}$ ${\mathrm{C}}^{13}$, ${86.52}_{77}$; for ${\mathrm{C}}^{12}$ ${\mathrm{D}}_3$ ${\mathrm{N}}^{14}$ ${\mathrm{C}}^{12}$, ${97.75}_{79}$; and for ${\mathrm{C}}^{12}$ ${\mathrm{D}}_3$ ${\mathrm{N}}^{14}$ ${\mathrm{C}}^{13}$, ${101.33}_{91}$. The molecular dimensions are: for C${\mathrm{H}}_3$CN, $d_{\mathrm{CH}}=1.092\mathrm{}$A, $d_{\mathrm{CC}}=1.460\mathrm{}$A, $d_{\mathrm{CN}}=1.158\mathrm{}$A, and ∠ HCH=109°8′; for C${\mathrm{H}}_3$NC, $d_{\mathrm{CH}}=1.094\mathrm{}$A, $d_{\mathrm{CN}}=1.427\mathrm{}$A, $d_{\mathrm{NC}}=1.167\mathrm{}$A, and ∠ HCH=109°46′. The nuclear coupling for ${\mathrm{N}}^{14}$ is -4.35 Mc/sec. in C${\mathrm{H}}_3$CN and is <|0.5| in C${\mathrm{H}}_3$NC.