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.