Effective collision cross section argon

The effective lifetime of an excited molecular level is tesip = 5 mbar) = 8 X 10" s and Tesip = 1 mbar) = 12 x 10" s for molecules with the mass M = 43 AMU in a gas cell with argon buffer gas at T = 500 K. Calculate the radiative lifetime, the collision-quenching cross section, and the homogeneous linewidth Av( >). 

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