Decay Dynamics of the Predissociating High Rydberg States of NO

Abstract

The dynamics of predissociating high molecular Rydberg states of NO below the lowest ionization threshold is computed in the presence of a weak external dc field using a quantum theory based on an effective Hamiltonian formalism. The core−electron interaction affecting the low l states (l ≤ 2) is taken into account by molecular quantum defect theory, while for the high l states (l ≥ 2), a long range multipolar expansion is used to describe the effect of the anisotropy of the molecular core. Time- and frequency-resolved ZEKE spectra are computed. In the energy range investigated, the decay kinetics of the ZEKE intensity is found to exhibit two time scales, which differ by more than an order of magnitude. The short decay constant typically falls in the submicrosecond range and is in agreement with previous experimental results and computations. In addition, our computations predict a long-time component, which decays in the tens of microseconds range. The two decay times are discussed in terms of the short and long range interseries dynamics, in terms of the strength of the external dc field, and in terms of the nature of the bottlenecks in phase space for a predissociating molecular core with a rather large rotational constant (B NO + = 1.9842 cm-1). It is found that for this particular case where all series are coupled to the fragmentation channels through a low l bottleneck, the predissociation process does not quench the long time component in the decay kinetics. The reason is that the interplay between the interseries coupling and the external dc field leads to a shift of the decay constants to larger values together with an enhancement of the weight of the long time component in the decay kinetics. Special attention is devoted to the role of the dipolar interaction and its synergy with the external dc field.

Dissociation and the Development of Spatial Correlation in a Molecular Ultracold Plasma

“…The deactivation of Penning partners to states of lower principal quantum number retards the climb to ionization, and increases the fraction driven down by electron collisions. Results derived from our coupled rate equation calculations accord with electron avalanche onset rates extrapolated from measurements made in a rubidium atom MOT at a series of lower densities by Robert-de-Saint-Vincent, et al [14] Rydberg states of NO predissociate with a rate that falls with increasing n. A widely used model developed by Bixon and Jortner [25][26][27] explains this variation, and accounts well for long-time plasma decay rates that we have observed experimentally in our system [20,24]. Taking predissociation rates as a function of n from this model, the calculation computes the fraction of excited molecules lost to neutral N þ O products, by integrating n-detailed decay rates over the avalanche ionization period appropriate to the selected value of n 0 .…”

Autoionizing Rydberg states of NO in strong electric fields

“…The lowest trace in Fig. 5͑a͒ 13 The only open channel for excitation lower than the saddlepoint energy via rotational states NЈϾ0 is excitation of a bound Rydberg state that decays by rotational autoionization into a lower NЈ Rydberg series. The near absence of signal below the saddlepoint energies shows that the rotational autoionization is very weak; note that the competing predissociation channel sets an upper limit to the time during which rotational autoionization can take place.…”

“…[3][4][5][6] The Rydberg series in NO and their lifetimes and couplings are quite well known. [7][8][9][10][11][12][13] Also other decay channels like predissociation are reported. 7,8,[14][15][16] However, important features of Rydberg electrons in a strong electric field have received little attention.…”

The Stark effect in the predissociating Rydberg states of NO

“…Photodissociation imaging studies of NO have also been performed by REMPI detection of the atomic fragments [27,28]. Vrakking and Lee measured the predissociation lifetimes of the v ¼ 0, np and nf states n ¼ 40-122 using a very high resolution laser system and delayed pulsed field ionisation detection [29,30], stimulating detailed studies of the decay dynamics and effects of fields [31][32][33]. Pratt [34] also studied predissociation of very high n states in the presence of electric fields using excitation from the same intermediate as our work.…”