First far-infrared high-resolution analysis of the ν2 and ν4 bands of phosgene 35Cl2CO and 35Cl37ClCO

A Fourier transform spectrum of phosgene (Cl2CO) has been recorded in the 17.3-μm spectral region at a temperature of 180 K and at a resolution of 0.00102 cm−1 using a Bruker IFS125HR spectrometer coupled to synchrotron radiation, leading to the observation of the ν2 and ν4 vibrational bands of the two isotopologues 35Cl2CO and 35Cl37ClCO. The corresponding upper-state ro-vibrational levels were fit using a Hamiltonian model accounting for the A-type Coriolis interaction linking the rotational levels of the 21 and 41 vibrational states. In this way, it was possible to reproduce the upper-state ro-vibrational levels to within the experimental uncertainty, i.e. ∼0.30 × 10−3 cm−1. Very accurate rotational and centrifugal distortion and interaction constants were derived from the fit, together with the following band centres: ν0(ν2, 35Cl2CO) = 572.526299(30) cm−1, ν0(ν4, 35Cl2CO) = 582.089026(30) cm−1, ν0(ν2, 35Cl37ClCO) = 568.951791(35) cm−1 and ν0(ν4, 35Cl37ClCO) = 581.758279(35) cm−1.