Ab initio and multipolar characterisation of the induced dipole surface for CH4–CH4: Application to dipole-forbidden absorption in the Titan’s atmosphere

Abstract

The present paper aims to further characterise the induced dipole surface for CH4–CH4 through either multipolar expansion or CCSD(T) ab initio calculations. Our calculations extend to evaluation of the collision-induced integrated intensity of absorption in the far infrared as well as to classical determination of the equilibrium constant for true bound methane dimer formation. Height profiles are simulated for the dimer mole fraction as well as for the portion of true bound dimer absorption in the integrated collision-induced absorption taking the Titan’s atmosphere as an example.