High resolution ro–vibrational analysis of molecules in doublet electronic states: the ν1 fundamental of chlorine dioxide (16O35Cl16O) in the X2B1 electronic ground state

Abstract

We report the spectrum of the ν₁ fundamental of chlorine dioxide centered in the infrared atmospheric window at 945.592 cm⁻¹ measured with essentially Doppler limited resolution at an instrumental line width of 0.001 cm⁻¹ using the Zürich prototype ZP2001 Bruker IFS 125 HR Fourier transform infrared spectrometer. The ro–vibrational line analysis is carried out with an improved effective Hamiltonian and a newly developed computer code ROVDES for the ro–vibrational spectra of open-shell free radical molecules including spin–rotation interactions. Accurate values of rotational, centrifugal and spin–rotational parameters were determined for ¹⁶O³⁵Cl¹⁶O in the vibronic ground state X²B₁ from more than 3500 ground state combination differences. The 7239 assigned transitions for the ν₁ fundamental with N^max = 76 and K^max_a = 26 provide a set of 32 accurate effective Hamiltonian parameters for the ν₁ fundamental (v₁v₂v₃) = (100) (21 rotational and centrifugal distortion parameters and 11 spin–rotational interaction parameters). This effective Hamiltonian (A – reduction and I^r – representation) reproduces 1703 upper state energies from the experiment with a root-mean-square deviation d_rms = 1.67 × 10⁻⁴ cm⁻¹ and the 7239 transition wavenumbers with d_rms = 3.45 × 10⁻⁴ cm⁻¹. Our results provide a considerable improvement over previous results with which we compare and should provide a benchmark for theoretical studies with applications to atmospheric spectroscopy and laser chemistry, which are discussed in relation to our spectra.