Pure Quadrupole Spectra of CH3I and CF3I Vapors

This paper first gives the theory of $\Delta J=0\mathrm{}$, $\Delta F=\pm 1$ transitions of symmetric top molecules having a nucleus with a large quadrupole moment on the axis. The manner in which the gaseous state spectrum converges on the pure quadrupole sold state spectrum as $J$ becomes infinite is discussed. Also is described an absorption experiment in which six quadrupole lines of C${\mathrm{H}}_3$I and one of C${\mathrm{F}}_3$I were observed in the region between 290 and 520 Mc/sec. The experiment yielded values of the quadrupole coupling constants of -1933.99±0.25 Mc/sec and -2142.5±1.8 Mc/sec respectively for C${\mathrm{H}}_3$I and C${\mathrm{F}}_3$I. These values are in agreement with previous values obtained elsewhere from rotational transitions.