Determination of fraction of molecules excited by laser IR radiation

To explain the observed excitation by laser IR radiation of moderate intensity (I = 1?10 MW/cm²) of the many rotational states (much greater than $\text{Ed}{}_{\mathrm{<mtext>01</mtext>}}\text{2}\text{hcB}$) it is suggested that mixing of the ground state components of the common symmetry type (“N-mixing”) take place. Estimation of the fraction of molecules excited by multiphoton processes is in satisfactory agreement with an experiment.