Vibrational relaxation of highly excited diatomics. II. HCl(v⩽7)+20 quenchers

120 vibrational relaxation rate constants kv,v−1Q are measured at 298 K for HCl (v⩽7) collisions with six diatomics: N2, CO, NO, HCl, DCl, and HF; three triatomics: CO2, N2O, NO2; and eleven polyatomics: CH4, C2H6, C3H8, iso-C4H10, CH3Cl, CH3F, CF4, SF6, CF3Cl, CF2Cl2, and CFCl3. For most quenchers, kQ increases with increasing v independent of whether the vibrational energy gap is reduced or increased. Large collisional relaxation probabilities for high v, of order 0.1 to 1 gas kinetic, are encountered for 11 of 20 quenchers. For Q=HC1 (v=0), the relaxation is shown experimentally to be mainly V–R,T for high v. The rates reflect a mix of effects due to dipole and dispersion interactions, energy gap, rotation, and complex formation, and present interesting problems of interpretation.