Absorber speed dependence of the coherence relaxation rate of the J=0–1 transition of N2O

Abstract

The coherence relaxation rate (T2) of the J=0 –1 transition of 15N2O has been examined using microwave transient techniques. The transient decays were analyzed by a model which considers the absorber speed dependence of the collisional relaxation process [S. L. Coy, J. Chem. Phys. 73, 5531 (1980)]. The decays were also analyzed by the standard speed independent model. In the speed dependent analysis, a linear absorber speed dependence of the form k(v)=k0+k1(v−v̄), where v̄ is the Boltzmann average speed, was assumed. Values of k0=0.0300(1) μs−1 mTorr−1 and k1v̄=0.0099(4) μs−1 mTorr−1 were determined. In the speed independent analysis a relaxation rate, k=0.029 22(6) μs−1 mTorr−1, was found. This corresponds to a pressure broadening parameter 1/2πT2 of 4.65(1) MHz/Torr. A zero pressure transition frequency and pressure dependent frequency shift parameter were also determined. They are 24 274.7865(1) MHz and +30(4) kHz/Torr, respectively. The experimental uncertainties reported above are two standard errors from linear least squares fits of k, k0, k1v̄, and transition frequency, vs sample pressure. The most significant systematic error is a 1% uncertainty in the pressure calibration which contributes an additional 1% error to the slopes determined from the linear least squares fits.