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.

• Received 30 March 1950

DOI:https://doi.org/10.1103/PhysRev.79.54