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

Abstract

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 (ΔE) is narrower than expected from the relation ΔE=C(F)1/2 (C=4∼6) [W. A. Chupka, J. Chem. Phys. 98, 4520 (1993)], and (2) the field ionization threshold was observed at n=82 (principal quantum number) for the p-series Rydberg states at a static dc field of 0.25 V/cm. From a MATI-2PFI spectrum obtained at F1=20 V/cm and F2=−33 V/cm, it has been found that the lifetimes of the p-series Rydberg states (n⩾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.