In paper I of this series, important deviations from an additive superposition of Lorentzian profiles were experimentally evidenced in the 00-degrees-3-00-degrees-0 band of CO2 in He. All the observed deviations are explained by the collision-induced line mixing effects which schematically transfer intensity from the wing of the band to its central part. The IOS approximation has been found to be insufficient while, the ECS approximation leads to theoretical predictions in good agreement with the experimental data over extended ranges of frequency and perturber pressure. However it must be emphasized that it has been necessary to resort to the method in current use for the determination of the fundamental rates, an ad hoc adjustement starting from the observed linewidths.