The Pure Rotational Spectrum of ICl

Frequencies and intensities of a number of lines of the J=3→4 rotational transition of ICl were measured and the spectrum analyzed. Constants obtained for ICl³⁵ are (in megacycles) Bₑ=3422.300, αₑ=16.060, eqIQI=-2930.0, eqClQCl=-82.5. The mass ratio Cl³⁵Cl³⁷ obtained from this spectrum is 0.9459801, which appears inconsistent with the most recent mass spectroscopic determination. The molecular dipole moment is approximately 0.65 ×{} 10^-18 e.s.u. from intensity measurements.