Rotational spectrum, structure, and intramolecular force field of the ArClCN van der Waals complex

The rotational spectrum of the ArClCN van der Waals complex has been assigned using pulsed Fourier transform microwave spectroscopy in a Fabry-Perot cavity with a pulsed supersonic nozzle as the molecular source. ArClCN is T-shaped and the data were fit to the Watson rotational parameters and an exact expression for the Cl and N nuclear quadrupole coupling. The spectroscopic constants for Ar35ClCN are A′′ = 6152.5411(21) MHz, B′′ = 1577.0362(8) MHz, C′′ = 1246.7514(6) MHz, τ1 = −576.0(2) kHz, τ2 = −97.28(8) kHz, τaaaa = −234.8(17) kHz, τbbbb = −55.97(10) kHz, τcccc = −21.60(7) kHz, χClaa = 37.9468(23) MHz, χClbb = −79.5239(20) MHz, χNaa = 1.6403(22) MHz, and χNbb = −3.4571(20) MHz. The centrifugal distortion constants are used to derive the intramolecular force field and a normal coordinate analysis is performed. The Cl nuclear quadrupole coupling tensor indicates that the field gradients in ClCN are slightly perturbed upon complex formation but not enough to proscribe their use in structural determinations of weakly bound complexes.