Linewidth parameters in the rotational spectrum of methyl cyanide

The linewidth parameters of some rotational components of the spectrum of methyl cyanide, J → J + 1 transitions (J = 0, 1, 2), were measured over a temperature range 195 ≤ T ≤ 300K and these experimental values were compared to available theoretical values. A multiple differentiation technique was employed in which derivatives of the rotational resonances were obtained in order to enhance resolution and to ascertain distortions within the line shapes. In some instances, high levels of modulation were required in order to obtain suitable resolution for the resonances and the method given by Netterfield was employed to correct for modulation broadening. The presence of hyperfine structure in the (J = 2 → J = 3) transition was found to produce overlapping of resonances which persisted to pressures less than 1 mTorr. Pressure ranges from 1 to 50 mTorr were explored in this investigation.