The influence of Rydberg states on the photodissociation of nitrous oxide

Abstract

The absolute photoabsorption cross section and the photoionization quantum efficiency of nitrous oxide have been measured from the ionization threshold to 21 eV, using a double ion chamber and monochromated synchrotron radiation, and these have enabled the absolute photodissociation cross section to be deduced. Variations in the photoionization quantum efficiency in the vicinity of a Rydberg state have allowed the competition between predissociation and autoionization in the decay of the super-excited state to be investigated. The photodissociation cross section exhibits prominent structure which correlates with known Rydberg series. Dispersed fluorescence techniques have been employed to identify the electronically excited neutral molecular species (N 2 B 3 g and NO B 2 ) formed through photodissociation of N 2 O. Fluorescence excitation spectra due to the N 2 B 3 g → A 3 + u and the NO B 2 → X 2 transitions following excitation of N 2 O have been recorded and the features in these spectra have been compared with the corresponding structure in the photodissociation spectrum. The N 2 B 3 g fragments are produced directly through photodissociation of the parent molecule. However, at low excitation energies the NO B 2 fragments are formed only through secondary reactions. The five Rydberg series converging onto the N 2 O + C 2 + g limit are considered in detail because each series exhibits a specific decay mechanism.

Dissociation dynamics of fluorinated ethene cations: from time bombs on a molecular level to double-regime dissociators

“…an alternative relaxation pathway, as in N 2 O + . 28,29 However, we will show that this is not always the case; long lived excited electronic states can in fact dissociate statistically when only the ground electronic state phase space is inaccessible to the system, and the long lifetimes allow for the statistical redistribution of the internal energy among the nuclear degrees of freedom.…”

“…Since the C-F bond is very strong, F loss cannot compete effectively on the ground electronic surface; the dynamics are dominated by the CF 3 + + CF, CF + + CF 3 and CF 2 + + CF 2 exit channels. However, if the first excited state is only weakly coupled to the ground state, which is hardly surprising given the 4-6 eV gap between the two states, F loss, [26]* - [28], becomes possible. This is not because the A ˜state converges to energetically disallowed excited state products, as was invoked in the non-statistical model for Sn(CH 3 ) 3 X 24 and methanol, 26 but because of large reverse barriers for the other competing processes on the excited state surface.…”

“…Third, in a particularly serendipitous turn, C 2 F 3 + , produced by non-statistical F-loss, undergoes a further sequential dissociation above 17 eV to form CF + , [26] * - [28] - [30]. However, sequential F-loss from the regime-one CF 2 + could interfere with the regime-two CF + signal, as evidenced by the small rise in the CF + abundance close to 18 eV.…”

Decay pathways of superexcited states of nitrous oxide

“…[20][21][22] Among these, the cross sections of the structured ionization region and their decay pathways have been investigated by Refs. [5], [7]- [9], and [17], and the competition between autoionization and predissociation of Rydberg states were clearly revealed. [9] Furthermore, the Rydberg states converg-ing to different ionic states are assigned and the mechanism of photoionization was studied.…”

“…Nitrous oxide has 22 electrons, and its groundstate electronic configuration can be written as (1σ) 2 (2σ) 2 (3σ) 2 (4σ) 2 (5σ) 2 (6σ) 2 (1π) 4 (7σ) 2 (2π) 4 . Extensive experimental works have been conducted to study the superexcited states of N 2 O, most of which were carried out by: photoabsorption, [4][5][6] photoionization, [7][8][9][10] photoelectron energy spectroscopy, [11][12][13][14] photoionization mass spectroscopy, [7,15,16] photon-induced fluorescence, [9,[17][18][19] and photoelectron-photoion coincidence spectroscopy. [20][21][22] Among these, the cross sections of the structured ionization region and their decay pathways have been investigated by Refs.…”