Real-time dissociation dynamics of the Ne2Br2 van der Waals complex

Pio, Jordan M.; Taylor, Molly A.; van der Veer, Wytze E.; Bieler, Craig R.; Cabrera, Jose A.; Janda, Kenneth C.

doi:doi:10.1063/1.3456550

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The dissociation of NO–Ar() from around threshold to 200 cm⁻¹ above threshold

We report an investigation of the dissociation of state NO–Ar at energies from 23 cm−1 below the dissociation energy to 200 cm−1 above. The NO product rotational distributions show population in states that are not accessible with the energy available for excitation from the NO ground state. This effect is observed at photon energies from below the dissociation energy up to approximately 100 cm−1 above it. Translational energy distributions, extracted from velocity map images of individual rot...

Sulfur K-edge photofragmentation of ethylene sulfide

We have investigated the photofragmentation properties of the three-membered ring heterocyclic molecule ethylene sulfide or thiirane, C2H4S, by time-of-flight mass spectroscopy. Positive ions have been collected as a function of photon energy around the S K ionization threshold. Branching ratios were derived for all detected ions, which are informative of the decay dynamics and photofragmentation patterns of the core-excited species. We present a new assignment of the spectral features around t...

We have characterized the vibrational predissociation (VP) of the Ne₂Br₂ van der Waals complex using time- and frequency-resolved pump-probe spectroscopy. After exciting Br₂ within the complex to a vibrational level 16 ≤ ν′ ≤ 23 in the B state, we follow the flow of halogen vibrational energy to the van der Waals modes in real time by recording the time-dependent behavior of Ne₂Br₂ (ν′), the NeBr₂ (ν′−m) intermediates, and the Br₂ (ν′−n) products. For Ne₂Br₂ (ν′ = 16–18), the only intermediate observed is NeBr₂ (ν′−1), and the majority of the final product is Br₂ (ν′−2), indicating the dissociation happens via two sequential direct VP steps. We fit the time-dependent behavior of these species to a sequential mechanism and extracted time constants for each step. For higher ν′ levels, the results show that the dissociation occurs via multiple pathways. Product Br₂ from levels lower than (ν′−2) becomes much more important, with products as low as (ν′−5) being observed. For ν′ = 21, we observe both NeBr₂ (ν′−1) and (ν′−2) intermediates. The intermediates have significantly different kinetics, with the decay rate of the (ν′−1) transient being nearly twice that of the (ν′−2) transient. Similarly, both Br₂ (ν′−2) and (ν′−3) are formed in almost equal amounts, but the (ν′−2) product formation rate is faster than the (ν′−3) rate. The broad vibrational product state distributions and multiple dissociation pathways indicate that intramolecular vibrational energy redistribution becomes increasingly important for ν′>19. We also report vibrational product state distributions for direct excitation to NeBr₂ 16 ≤ ν′ ≤ 23. For NeBr₂, the dominant product channel is Br₂ (ν′−1) for all initial ν′ studied, consistent with this complex dissociating primarily via direct VP.

Article Outline

INTRODUCTION
EXPERIMENTAL
RESULTS
1. Excitation spectra
2. Probe spectra
  1. NeBr₂ probe spectra
  2. Ne₂Br₂ probe spectra
  3. Vibrational product state distributions
3. Delay scans
DISCUSSION
1. Model for predissociation dynamics
2. Energy changes with ν′
3. Dissociation mechanism for low ν′ levels
4. Dissociation mechanism for high ν′ levels
5. Comparison to NeBr₂ predissociation lifetimes
6. Comparison to theory
7. Comparison to other Ne₂X₂ complexes
CONCLUSION

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KEYWORDS and PACS

Keywords

bromine, excited states, intramolecular forces, neon compounds, predissociation, time resolved spectra, vibrational states

PACS

33.80.Gj

Diffuse spectra; predissociation, photodissociation
33.15.Mt

Rotation, vibration, and vibration-rotation constants
31.50.Df

Potential energy surfaces for excited electronic states
34.20.-b

Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
33.20.Tp

Vibrational analysis

ARTICLE DATA

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http://link.aip.org/link/doi/10.1063/1.3456550

PUBLICATION DATA

ISSN:

0021-9606 (print)

1089-7690 (online)

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American Institute of Physics

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