Field induced ion-pair formation from ICl studied by optical triple resonance

Abstract

Multiphoton pathways to the ion-pair states of ICl, at energies close to dissociation, are presented. These very high vibrational levels (v P 104) are detected in the I`and Clc hannels by pulsed Ðeld ionisation. Using a variable time delay before Ðeld ionisation, ion-pair states up to 50 cm~1 below the dissociation limit are shown to survive for at least 2 ls, indicating a stabilisation process analogous to that operating in high Rydberg electronic states. The atomic ion production signal is highly structured both above and below the free ion threshold, indicating the role of doorway states which are coupled to the dense ion-pair manifold near dissociation. This initial coupling appears to be very efficient and competes successfully with radiative decay and further up-pumping.

Observation of Coherent Wave Packets in a Heavy Rydberg System

“…A remarkable difference from other potentials is the infinite number of bound states of nuclear motion (rovibrational states) supported close to the dissociation threshold; potentials associated with a covalent bond typically show an asymptotic shape of V n ϳ 1͞r n with n 3 6 and consequently support a finite number of bound states. A connection between the standard treatment of molecules on the one hand, using potentials of electronic states and quantized nuclear motion described by vibrational and rotational quantum numbers y and J, and an ion-pair Rydberg model on the other was established by identifying the effective principal quantum number n with y 1 J 1 1 while the angular momentum of the Rydberg system ᐉ corresponds to J [2].Ion-pair states have been observed in two different regimes: deep in the potential [3,4], where the ionic electron configuration is only approximate due to a major interaction with covalent configurations, and at threshold, where no structure within the ion-pair configuration is observed [5]. Threshold-ion-pair-production spectroscopy (TIPPS) has been used to determine the ion-pair dissociation limit in H 2 [6].…”

“…Ion-pair states have been observed in two different regimes: deep in the potential [3,4], where the ionic electron configuration is only approximate due to a major interaction with covalent configurations, and at threshold, where no structure within the ion-pair configuration is observed [5]. Threshold-ion-pair-production spectroscopy (TIPPS) has been used to determine the ion-pair dissociation limit in H 2 [6].…”

Continuity of heavy Rydberg behaviour in the ungerade ion-pair states of H 2

“…It will be difficult to access this region ðE b ¼ 0-3000 cm À1 Þ by transitions directly from the ground state or through intermediate states using optical double resonance techniques. However, as noted above, access is known to be possible through electronic Rydberg states which are coupled to many of the ion-pair states; this approach is the basis of the Threshold Ion-pair Production Spectroscopy (TIPS) [24] and Zero Ion Kinetic Energy (ZIKE) techniques [25,26]. This high energy region, where HR states are found to be long-lived (s $ 10 À6 s), can also be studied using pulsed excitation techniques to prepare a coherent superposition of states and observing the evolution of the wave packets thus produced [27,28].…”

Dissociation dynamics of ion-pair states of Cl2at principal quantum numbers beyond 1500

“…The observation of ion-pair states of high principal quantum number by direct photoexcitation from the ground state is usually hindered by extremely small Franck-Condon factors and is intrinsically linked to complex interactions between dissociation and ionization channels at short internuclear distances [1][2][3]10,[12][13][14]. So far, interactions between series of ion-pair states converging to different ion-pair dissociation thresholds have neither been observed nor discussed in the literature, presumably because the amplitudes of ion-pair wave functions are very small at short internuclear distances, where the channel interactions take place.…”

“…We report here on the observation of ion-pair states of Cl 2 which reveal the existence of such interactions. Cl 2 is an ideal system to study ion-pair states [11][12][13][14][15][16][17][18][19] because the very large electron affinity of the Cl atom makes it possible to observe these states over a wide energy range below the first dissociative ionization threshold. Moreover, Cl + possesses several low-lying electronic states, which offers the possibility, exploited in the present study, of studying interactions between different series of ion-pair states.…”