$T_{2}$ RELAXATION TIMES FOR HCN

$^{1}$T. Anderson, C. Gudeman, T. Dixon, and P.C. Woods, J. Chem. Phys. 80, 1332 (1980). $^{2}$S. Green, Astrophys, J. 201, 366 (1975).Author Institution:Polarization relaxation times $(T_{2})$ have been measured for the J = 6, 9, and 10 $\ell$-doublet transitions in the (01^{\prime}0) vibrational level of HCN by means of microwave transient emission. Also, $T_{2}$ values for relaxation induced by He, $H_{2}$, and $CH_{3}F$ are obtained for the J = 6 transition. The dephasing cross sections for foreign gas collisions are consistent with the force laws operative in each case. The $HCN-H_{2}$ result provides a comparison with the recently measured cross section of the isoelectronic molecular ion system, $HCO^{+} - H_{2},^{1}$ and confirms the prediction of $Green^{2}$ that rotational relaxation rates ire only moderately faster for molecular Ions. The HCN-self relaxation data will be discussed in terms of the two level model used 1n various theoretical treatments