Abstract: The integrated intensities of the collision-induced absorption of the $\nu _{2}$ band of $^{12}$CH$_{4}$ perturbed by Ar have been calculated  theoretically using the ab initio calculations, and the value of the quadrupole transition moment we obtained is $\langle {0| Q |\nu _2 } \rangle  =5.226ea_0^2 $. The corresponding experimental value obtained from $^{12}$CH$_{4}$--Ar spectra is $| {\langle {0| Q |\nu _2 } \rangle } |=4.931ea_0^2 $. Ignoring vibration--rotation interaction and Coriolis interaction, and considering both the theoretical approximations and experimental uncertainties, the agreement can be regarded as good, thus confirming that the enhancement is due to the quadrupole collision-induced mechanism. 

Key words: collision-induced absorption, $\nu_2$ fundamental band, quadrupole transition moment