One- and two-pulsed field ionization spectra of NO: High-lying Rydberg states near ionization threshold

High-lying rotational Rydberg states (p series) of NO near the ionization threshold were prepared by two-color (1+1') resonant excitation, and then detected by a ZEKE (zero kinetic energy) electron technique as well as by a MATI (mass analyzed threshold ion) technique using one-and two-pulsed field ionization (abbreviated by 1PFI and 2PFI, respectively). The MATI-2PFI spectrum has been interpreted in terms of a single progression due to p-series Rydberg states (n = 37-48) converging into the ion core with N+ = 11, perturbed by the d-series Rydberg states converging into N+ = 12. From a ZEKE-1PFI spectrum obtained at a high field strength of F= -33 V/cm, it has been found that (1) the band width (Delta E) is narrower than expected from the relation Delta E = C(F) (1/2) (C=4 similar to 6) [W. A. Chupka, J. Chem. Phys. 98, 4520 (1993)1, and (2) the field ionization threshold was observed at n = 82 (principal quantum number) for the p-series Rydberg states at a static de field of 0.25 V/cm. From a MATI-2PFI spectrum obtained at F-1=20 V/cm and F-2 = -33 V/cm, it has been found that the lifetimes of the p-series Rydberg states (n greater than or equal to 37) below the field ionization threshold are lengthened at the same static electric field. These experimental results may be interpreted in terms of two factors; one is the lifetime lengthening due to the Stark mixing between the lower and the higher l states, and the other is the rotational coupling of between a low-n high-N+ state and a high-n low-N+ state, lengthening the apparent lifetime of the low-n high-N+ state. (C) 1997 American Institute of Physics.