Pressure studies of subthreshold photoionization: CH3I, C2H5I and C6H6 perturbed by Ar and SF6

Subthreshold photoionization spectra of CH3I doped into Ar and SF6, and C2H 5I and C6H6 doped into SF6, are reported for variations in both the dopant number density rho (D) and perturber number density rho (p). The rho (D) an d rho (p) dependence of the subthreshold structure is discussed in terms of the excited state processes of electron attachment and associative ionizat ion. The variation in the subthreshold photocurrent as a function of rho (D ) and rho (p) leads to the determination of the effective rate constants fo r these processes. These constants are then analyzed with respect to the pr operties of the excited dopant Rydberg state. For CH3I, the variations in t he effective rate constants are discussed in terms of ground-state dopant a nd perturber properties. (C) 2001 Elsevier Science B.V. All rights reserved .