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

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 Nmax = 76 and Kmaxa = 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 Ir – representation) reproduces 1703 upper state energies from the experiment with a root-mean-square deviation drms = 1.67 × 10−4 cm−1 and the 7239 transition wavenumbers with drms = 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.