Rotational spectra of twenty-one vibrational states of [35Cl]-and [37Cl]-chlorobenzene

The rotational spectra of [³⁵Cl]- and [³⁷Cl]-chlorobenzene (C₆H₅Cl) have been studied from 2 to 18 GHz and 130-360 GHz, resulting in the measurement, assignment, and least-squares fitting of almost 40,000 transitions of twenty-one vibrational states. Previously measured [³⁵Cl]- and [³⁷Cl]-chlorobenzene ground-state transitions were combined with newly measured transitions and fit to A-reduced, partial sextic Hamiltonian models with low-error (σ_{total fit} <0.05 MHz). Analysis of the 2-18 GHz spectrum allowed for refinement of the nuclear hyperfine coupling constants for the ground-state spectra of both isotopologues, while measurement of the 130-360 GHz spectrum provided sufficient information to determine the sextic centrifugal distortion constants of the ground states for the first time. From these millimeter-wave data collected at room temperature, the spectroscopic constants for the lowest-energy fundamentals of [³⁵Cl]-chlorobenzene (ν₂₀, ν₃₀, ν₁₁, ν₁₄, ν₁₉, ν₂₉ and ν₁₈) and [³⁷Cl]-chlorobenzene (ν₂₀, ν₃₀, ν₁₁) were determined. As with previous studies of chloroarenes, the computed (B3LYP/6-311+G(2d,p)) spectroscopic constants show quite close agreement with the experimentally determined values.