Microwave pulse techniques have proved to be very useful to obtain informations about coherence decay rates and population transfer rates in gas phase. the coherence decay rates have been measured by a technique which involves the detection of the transient emission signal of the molecular sample following an intense microwave pulse. the (π-τ-π/2) pulse sequence technique has been used to extract informations about population transfer rates. the experimental results on 1-doublet transitions of HCN and HCCCN perturbed by H2,D2 and He are given. the theoretical results obtained from the perturbative approach to collision dynamics have also been computed, and compared with the experimental results. for the 1-doublet transitions of HCN, the population decay rates have found to be considerably less than the corresponding coherence decay rates.