  Spectra of methyl cyanide were recorded to analyze interactions in low-lying
vibrational states and to construct line lists for radio astronomical
observations as well as for infrared spectroscopic investigations of planetary
atmospheres. The rotational spectra cover large portions of the 36$-$1627 GHz
region. In the infrared (IR), a spectrum was recorded for this study in the
region of 2$\nu _8$ around 717 cm$^{-1}$ with assignments covering 684$-$765
cm$^{-1}$. Additional spectra in the $\nu _8$ region were used to validate the
analysis.
  The large amount and the high accuracy of the rotational data extend to much
higher $J$ and $K$ quantum numbers and allowed us to investigate for the first
time in depth local interactions between these states which occur at high $K$
values. In particular, we have detected several interactions between $v_8 = 1$
and 2. Notably, there is a strong $\Delta v_8 = \pm1$, $\Delta K = 0$, $\Delta
l = \pm3$ Fermi resonance between $v_8 = 1^{-1}$ and $v_8 = 2^{+2}$ at $K$ =
14. Pronounced effects in the spectrum are also caused by resonant $\Delta v_8
= \pm1$, $\Delta K = \mp2$, $\Delta l = \pm1$ interactions between $v_8 = 1$
and 2. An equivalent resonant interaction occurs between $K$ = 14 of the ground
vibrational state and $K$ = 12, $l = +1$ of $v_8 = 1$ for which we present the
first detailed account. A preliminary account was given in an earlier study on
the ground vibrational state. From data pertaining to $v_8 = 2$, we also
investigated rotational interactions with $v_4 = 1$ as well as $\Delta v_8 =
\pm1$, $\Delta K = 0$, $\Delta l = \pm3$ Fermi interactions between $v_8 = 2$
and 3.
  We have derived N$_2$- and self-broadening coefficients for the $\nu _8$,
2$\nu _8 - \nu _8$, and 2$\nu _8$ bands from previously determined nu4 values.
Subsequently, we determined transition moments and intensities for the three IR
bands.
