Water ortho-para conversion by microwave background radiation in space

A theoretical model of water ortho-para conversion induced by blackbody radiation in space is developed. The model is based on two main ingredients: the mixing of water ortho and para states by a hyperfine spin-rotation interaction in the molecule and the interruption of this mixing by surrounding blackbody radiation. The model predicts the lifetime of water spin isomers tau = 2.7 Myr for radiation with a temperature of 100 K and tau = 1.3 Gyr for microwave background radiation. The time dependence of the ortho-to-para ratio (OPR) of water molecules interacting with microwave background radiation is determined. The temperature dependence of the stationary OPR predicted by the model is found to be different from the usually accepted OPR for water spin isomers.

Automated summary

A theoretical model is developed to explain water ortho-para conversion induced by blackbody radiation in space, predicting the lifetime of water spin isomers and the time evolution of ortho-to-para ratio. The temperature dependence of the stationary OPR as predicted by the model differs from the commonly accepted OPR for water spin isomers.