Evidence of true bound and metastable dimers and trimers presence in high temperature water vapor spectra

We consider the ratio between true bound and metastable states of small water clusters in water vapor. Reanalysis of water vapor spectra recorded at 650 K and pressures up to 110 atm in the OH fundamental stretching region was performed using an improved spectroscopic model that revealed manifestations of dimers and trimers in both true bound and metastable states. Dimer and trimer quantities in both states were determined in the model by the corresponding equilibrium constants which were variable coefficients in equations of integrated spectral intensity, of absorption coefficient, and of water vapor thermodynamic state. The obtained constants are in good agreement with the previously known values, including agreement with those obtained from the empirical high-precision thermodynamic water vapor data. The analysis confirms that amounts of bound dimers and trimers are significant even at supercritical temperature.

► New quantitative information is obtained from the 2500-5000 cm−1 high-T water vapor spectra. ► True bound and metastable water dimer and trimer equilibrium constants are found. ► The significance of bound dimer contribution to atmospheric continuum is confirmed.