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(ν_2, ³⁵Cl₂CO) = 572.526299(30) cm⁻¹, ν₀(ν_4, ³⁵Cl₂CO) = 582.089026(30) cm⁻¹, ν₀(ν_2, ³⁵Cl³⁷ClCO) = 568.951791(35) cm⁻¹ and ν₀(ν₄, ³⁵Cl³⁷ClCO) = 581.758279(35) cm⁻¹.