The formation of fluorescent and metastable fragments by photoexcitation of some diatomic molecules in the vacuum ultraviolet region

Abstract

The formation of fluorescent and metastable fragments from four diatomic molecules, i.e. O2, N2, NO and CO, has been investigated in the vacuum ultraviolet region. The neutral particles are detected by using a microchannel plate stack, where retarding electric potentials prevent charged particles from reaching the detector. Every diatomic molecule investigated here shows the formation of fluorescent and metastable fragments in particular photon energy regions. Three Rydberg states of O2 converging to O2+(a 4Πu) undergo both neutral dissociation processes forming fluorescent [O+(4S)]3s 3S1 and metastable [O+(4S)]3s 5S2; the yield curve for each fragment is determined. Direct and cascade formation of the fluorescent [N+(3P)]3s 4P fragment from N2 are separated, and it is found that the dissociation of the 4s σ Rydberg state converging to N2+(C 2Σu+) preferentially produces [N+(3P)]3p fragments, but not or weakly the [N+(3P)]3s 4P fragment. High -n Rydberg states converging to NO+(c 3Π) and CO+(D 2Π) undergo neutral dissociation described by the core ion model, resulting in large peaks for neutral particle formation.

Long-lived, highly excited neutral hydrogen atom production following oxygen 1s photoexcitation of gas-phase water molecules

“…Using a similar experimental technique neutral excited N * and H * fragments have been detected following N 1s excitation/ionization in N 2 [21,22], Cl 2p excitation/ionization in HCl [23], and valence photoexcitation of O 2 , N 2 , NO, and CO [24]. Neutral excited N * fragments have also been detected following the dissociation of N 2 in strong laser fields [25].…”

Neutral photodissociation of superexcited states of molecular iodine

“…In contrast, only very few studies have directly detected the high-n Rydberg fragments excited molecules using detectors based on field ionization. [6][7][8][9] In this study we report resonant excitation of I 2 by two photons from an ArF laser ͑193 nm͒ into molecular Rydberg states converging on the I 2 + ͑B 2 ⌺ g + ͒ ionic state ͑see Fig. 1͒.…”

“…It has been generally accepted that the SESs leading to the products in reaction ͑1c͒ are high-n molecular Rydberg states converging on each ion state, although non-Rydberg SESs have also been observed. 3 High-n Rydberg fragments from neutral dissociation of SESs have been directly observed in a small number of experiments; [4][5][6][7][8][9] however, the translational energy and angular distributions of these fragments were not measured. Extracting these data yields information on the dissociative ionic potential energy curves ͑PECs͒ as the PECs of the high-n Rydberg molecules are parallel to the ionic PECs to which they converge.…”

“…For example, based on earlier work, [11][12][13] Hikosaka et al 8 observed fluorescing and metastable oxygen atoms following excitation of O 2 near 22 eV using synchrotron radiation. The yield curves of excited neutral particles exhibited peaks at Rydberg states converging to the ionic core states O 2 + ͑B 2 ⌺ g − ͒ and O 2 + ͑c 4 ⌺ u − ͒, and the yields were strongly enhanced for high values of n. These authors subsequently employed the same technique to observe metastable Rydberg fragments from the neutral dissociation of N 2 , NO, and CO. 9 Loock et al 14 detected Rydberg states of I atoms in the range of n =6-8 from the dissociation of HI at 13.39 and 15.59 eV. The Rydbergs were observed due to their ionization by additional photons, and ion imaging was used to determine the kinetic energy release.…”

High Resolution Multiphoton Spectroscopy by a Tunable Free-Electron-Laser Light

“…By detection of neutral metastable (MS) fragments which are produced exclusively by the fluorescence decay or neutral dissociation of superexcited states, the spectrometer can be bypassed to make spectroscopy dependent on FEL resolution only. The MS states are long lived either because the fragments are highly excited, or because decay of the MS states to the ground state violates the dipole selection rule [23]. The MS species can be easily discriminated against charged particles and they can carry enough internal energy to trigger the microchannel-plate detector.…”