The density of reactive levels in NO2 unimolecular decomposition

Ionov, S. I.; Davis, H. S.; Mikhaylichenko, K.; Valachovic, L.; Beaudet, Robert A.; Wittig, C.

doi:10.1063/1.467403

Cited by 57 publications

(64 citation statements)

References 130 publications

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“…Therefore, even by using v Ӎ0.5 level per cm Ϫ1 , this corresponds to an expected maximum of three observable levels per cm Ϫ1 which is three times less than the density of levels actually observed. 17,36 High-resolution experiments in this energy range should allow us to determine if the observed levels are all levels belonging to the X 2 A 1 and Ã 2 B 2 electronic states and if the number of Jϭ3/2 lines is twice the number of Jϭ1/2 lines, as expected for strong rovibronic interactions. The behavior of NO 2 around its dissociation limit is far from being understood and the question about the existence of a rovibronic chaos in this energy range is very exciting, taking into account its implication in the understanding of the photodissociation process just above the dissociation limit.…”

Section: Discussionmentioning

confidence: 99%

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The visible excitation spectrum of jet cooled NO2: Statistical analysis of rovibronic interactions

Delon

Georges

Jost

1995

The Journal of Chemical Physics

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We have recorded the high resolution (150 MHz) excitation spectra of NO2 molecules cooled in a supersonic jet in two energy ranges: 16 000–19 362 cm−1 [‘‘yellow’’ range, see R. Georges, A. Delon, and R. Jost, J. Chem. Phys. 103, 1732 (1995), hereafter referred to as paper I] and 23 326–23 945 cm−1 (‘‘blue’’ range). In this paper we are interested mainly in the rovibronic properties of about 1500 rotational levels (N=1, K=0, J=1/2, and J=3/2) observed in these two ranges. Among these levels about 480 are observed via the so-called extra lines, i.e., the lines which are observable because of rovibronic couplings between bright levels (N=1, K=0, 2B2 vibronic character) and nearby dark levels. These rovibronic couplings result mainly from second order spin–orbit and orbit–rotation interactions which have been evidenced previously by Zeeman effect and anticrossing experiments [A. Delon, P. Dupré, and R. Jost, J. Chem. Phys. 99, 9482 (1993)]. By comparing the average matrix element of rovibronic interactions occuring for N=1, K=0 (J=1/2 and J=3/2), and for N=3, K=0 (J=5/2 and J=7/2) we can exclude a significant contribution from Coriolis interactions. A model of small random matrices constructed by using the properties of the above mentioned rovibronic Hamiltonian (density of states, selection rules, and matrix elements) allowed us to reproduce the observed statistical properties of the rovibronic states: average number of extra lines per vibronic band, distribution of intensities, Fourier transform analysis, next-neighbor spacing distribution, hierarchical tree analysis, and intensity and energy correlations between J=1/2 and J=3/2 lines. All these properties confirm that the second-order spin–orbit interaction is responsible for most of the observed extra lines for low rotational levels N=1 and N=3, K=0. As a result, the average reduced rovibronic matrix element is 0.6∓0.1 cm−1 and 0.7∓0.1 cm−1 for the yellow and blue ranges, respectively. The yellow range result is in reasonable agreement with the results obtained previously under magnetic field experiments. We also derive analytical formulas applicable for the weak interaction regime and discuss the relation between the observed distribution of matrix elements and the true distribution.

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Section: Discussionmentioning

confidence: 99%

“…The situation just below the first dissociation limit ͑25 130 cm Ϫ1 ͒ seems to be quite different. 17,36 Extrapolation of our calculated density of states 1 at this energy leads to a vibronic density v Ӎ0.37 level per cm Ϫ1 . This density can be compared to the one calculated by Toselli et al: 35 Ӎ0.50 level per cm Ϫ1 .…”

Section: Discussionmentioning

confidence: 99%

The visible excitation spectrum of jet cooled NO2: Statistical analysis of rovibronic interactions

Delon

Georges

Jost

1995

The Journal of Chemical Physics

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“…The density of quasibound levels assumed in the calculations reflects that observed in LIF spectra in the region 0-5 cm -1 below threshold. 30,31 To account for electronic degeneracies of the fragments, 29 we set N ) 4 in eq 7 and obtain 〈Γ(E)〉F ) 0.64. …”

Section: Probes Of Interferences Among Overlapping Resonances In mentioning

confidence: 99%

Unimolecular Reaction of NO₂: Overlapping Resonances, Fluctuations, and the Transition State

Reid

Reisler

1996

J. Phys. Chem.

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The unimolecular decomposition of expansion-cooled NO 2 at excess energies 0-3000 cm -1 is described with emphasis on the manifestations of overlapping resonances. When NO 2 is excited to energies above dissociation threshold, overlapping resonances interfere and give rise to final state-selected spectra which depend on the monitored final state of the NO product. The differences among the spectra diminish with the degree of incoherent superposition (e.g., thermal averaging). In this article, we describe the experimental manifestations of overlapping resonances in the case of barrierless unimolecular reactions and how they relate to transition state theories. We treat the unimolecular reaction of NO 2 using resonance scattering theory combined with random matrix formalism and distinguish between the near-threshold region where the transition state is loose and dissociation at higher excess energies where the transition state has tightened significantly. The final state-selected spectra and their dependence on the degree of resonance overlap are simulated in a qualitative way. Experimentally, fluctuations are observed in the line shapes, positions, and intensities in the spectra; the rotational and vibrational NO state distributions; the spin-orbit states of the oxygen atom correlated with specific quantum states of NO; and the state-specific rates. We show how the patterns of fluctuations in the rotational distributions allow the distinction between the loose and tight transition state cases and discuss the evolution of the excited complex from transition state to final products. In spite of the fluctuations, the averaged results agree well with the predictions of statistical theories, and implications for the transition state and the adiabatic evolution of the NO degrees of freedom are discussed. Even when the product state distributions agree with the predictions of specific statistical models, caution should be exercised in inferring properties of the transition state, due to the unaccounted influence of final state interactions beyond the transition state.

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“…near DO is modest (<1 per cm-1). [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Since in addition the number of product channels is relatively small, at least at low excess energies I?, quantum state-specific effects are expected. Above DO the spectrum of NO2, which remains highly structured, can be described in terms of coherently overlapping resonance^.^^^,^^ The state-selected resonance widths gradually increase with I?,7 as the dissociation lifetime decreases from a few picosecond just above DO to 1 ps at E?…”

Section: Introductionmentioning

confidence: 99%

Fully Quantum-State Resolved Study of NO2 Photodissociation: Correlated NO(2.PI..OMEGA., .nu. = 0,J,.LAMBDA.) + O(3Pj) Distributions

Sanov¹,

Bieler²,

Reisler³

1995

J. Phys. Chem.

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Relative O(3Pj=~,~,~) spin-orbit populations correlated with specific N0[2nQ=l/2,3/2; Y = 0; J; A = II(A'), n(A")] product states were obtained following photolysis of NO2 at excess energies Zi ? = 390, 425, and 1054 cm-I. These fully quantum state-resolved measurements were carried out by recording spatial profiles of recoiling N0(213~,J,A) products using polarized radiation for photolysis and state-selective laser ionization detection. The relative O(3P,) populations correlated with each N0(213~,J,A) state show marked fluctuations at each excess energy as a function of rotational state and A-doublet component. The relative populations also fluctuate as a function of excess energy. The O(3Pj) spin-orbit population ratios, when averaged over all measurements, exhibit distributions that are colder than statistical, in agreement with previous results. In particular, we find that, on average, O(3P~):O(3P2) population ratios correlated with the ground N0(2171/2) state are colder than the corresponding ratios correlated with the excited NO(TI3/2) spin-orbit state. These results are in agreement with the state-specific calculations of Katigiri and Kat0 [J. Chem. Phys. 1993, 99, 88051 and are discussed in terms of long-range nonadiabatic transitions among electronic states correlating asymptotically with different spin-orbit states of the ground NO(TI) + O(3P) dissociation channel.

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The density of reactive levels in NO2 unimolecular decomposition

Cited by 57 publications

References 130 publications

The visible excitation spectrum of jet cooled NO2: Statistical analysis of rovibronic interactions

The visible excitation spectrum of jet cooled NO2: Statistical analysis of rovibronic interactions

Unimolecular Reaction of NO₂: Overlapping Resonances, Fluctuations, and the Transition State

Fully Quantum-State Resolved Study of NO2 Photodissociation: Correlated NO(2.PI..OMEGA., .nu. = 0,J,.LAMBDA.) + O(3Pj) Distributions

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The density of reactive levels in NO2 unimolecular decomposition

Cited by 57 publications

References 130 publications

The visible excitation spectrum of jet cooled NO2: Statistical analysis of rovibronic interactions

The visible excitation spectrum of jet cooled NO2: Statistical analysis of rovibronic interactions

Unimolecular Reaction of NO2: Overlapping Resonances, Fluctuations, and the Transition State

Fully Quantum-State Resolved Study of NO2 Photodissociation: Correlated NO(2.PI..OMEGA., .nu. = 0,J,.LAMBDA.) + O(3Pj) Distributions

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Unimolecular Reaction of NO₂: Overlapping Resonances, Fluctuations, and the Transition State