Acetone photophysics in seeded supersonic molecular beams

The photodynamics of acetone and some other simple aliphatic ketones in the mt* state are discussed in the light of recent results obtained in seeded supersonic beams. The Born-Oppenheimer approximation is used to describe the sequence of events beginning with light absorption and ending in molecular fragmentation. Intersystem crossing is shown to be an important process even for the isolated molecule. Its rate increases with the internal energy and may be related to the density of states in the triplet state. For all molecules studied so far, the results can be rationalized by assuming that dissociation takes place on the triplet surface, the SI surface being stable in the energy range pertinent to these experiments (up to 35,000 ern-I above the ground state). Fluorescence spectroscopy may be used also to detect small clusters. In the case of acetone, their presence is indicated by the decrease in the intensity of some spectral lines as a function of cooling efficiency. The results are used to estimate an upper limit for the van der Waals binding energies. posal in the fragments of dissociating molecules, including vector correlations. The first aspect has been extensively discussed, experimentally and theoretically, in the case of pyrazine.v" and also of carbonyl compounds, such as methylglyoxal and biacetyl,? propynal," butynal,? and acetaldehyde,'? which are more closely related to the topic of this paper. Dissociation dynamics were mostly studied for three-or four-atom molecules: ICN, 15 H 20,16 HONO,17 and H 202.18,19 Some larger molecules were also studied, notably methylnitrite" and tertbutyl nitrite."Both aspects were extensively studied in the case of formaldehyde, for which the energy disposal into the different fragments was carefully measured." In the case of formaldehyde, spectroscopic assignments are reasonably well established, and perturbations can be analyzed to yield interstate interactions. Since photochemistry often involves curve-crossing (in the Born-Oppenheimer approximation), this molecule appears at present to provide the best link between spectroscopic and dynamic (time-resolved) studies.

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“…As discussed in Ref. 37, the gradual decrease of the rate is compatible with the theory briefly outlined above (cf. Eq.…”

Section: Methodssupporting

confidence: 88%

“…6-9.36 Here we quote the main features of the analysis, more details may be found in Ref. 37. Initial excitation is assumed to entail a single SI state, and NT1 states.…”

Section: Methodsmentioning

confidence: 99%

Photodynamics of Small Aliphatic Ketones in a Supersonic Jet Expansion

Haas

Zuckermann

1989

Israel Journal of Chemistry

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“…Figure 2 illustrates the potential energy levels of the acetone molecule assembled from the available spectroscopic information. 5,8,11,[18][19][20] Only those states relevant to this study are shown. With the wavelengths employed in this study, the S 1 state can be accessed by one photon of 259 nm; two photons of 390 nm will access the 3s Rydberg state, while two photons of 259 nm or three photons of 390 nm can access the Rydberg states near the ionization continuum.…”

Section: Experimental Methodsmentioning

confidence: 99%

Ultrafast dissociation dynamics of acetone: A revisit to the S1 state and 3s Rydberg state

Zhong

Poth

Castleman

1999

The Journal of Chemical Physics

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Because of the dispute in the literature over the dissociation rate and energy partitioning of the acetone molecule upon photoexcitation to the S 1 state (*←n) and 3s Rydberg state (3s←n), we have remeasured the lifetime of acetone ͑also d 6 -acetone͒ on the S 1 and 3s surfaces by a femtosecond time-resolved multiphoton ionization technique, coupled with a reflectron time-of-flight mass spectrometer. The measured dissociation rate of acetone on the S 1 surface is prompt, and the acetyl radical is long lived. The lifetime of acetone on the 3s surface is measured to be 3.2Ϯ0.4 ps ͑6.0Ϯ0.5 ps for d 6 -acetone͒. The dissociation rate of acetyl is approximately 1.7 ps ͑2.5 ps for d 3 -acetyl͒ from the curve fitting. This agrees well with the Rice-Ramsperger-Kassel-Marcus theory predicted lifetime of 1.0 ps ͑1.9 ps for d 3 -acetyl͒ when the internal excitation energy of the acetyl radical is treated by a statistical-adiabatic-impulsive model.

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“…This transition has also been observed by threshold electron-impact spectroscopy by van Veen et al 43 However, the maximum could not be reported in that study because of the strong n→3s transition to the 1 1 B 2 Rydberg state near 6.35 eV, 7,10,40,41,43 which is in agreement with various theoretical predictions. 2,4,42 Interestingly in gas-phase photolysis studies, [13][14][15][16][17][18][19][20][21][22] the dissociation of acetone into two methyl radicals and a CO has been attributed to this Rydberg transition.…”

Section: A Electronic Energy Lossesmentioning

confidence: 99%

“…The electronic spectroscopy of acetone 2-10 is of further particular interest to increase our understanding of the mechanisms of photolysis, 11,12 especially regarding three-body dissociation dynamics. [13][14][15][16][17][18][19][20][21][22] Strong dissociation channels leading to the formation of various molecular fragments have been reported for many electronic states. In the study of the electronic spectrum of acetone, both experiment 5,6,23 and theoretical calculations 2 have revealed the existence of a coupling between some Rydberg states and the →* valence state of the molecule.…”

Section: Introductionmentioning

confidence: 99%

Low-energy electron-energy-loss spectroscopy of condensed acetone: Electronic transitions and resonance-enhanced vibrational excitations

Lepage

Michaud

Sanche

2000

The Journal of Chemical Physics

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We report electron-energy-loss spectroscopy, within the incident electron energy range 1 to 19 eV, of solid films of acetone condensed at 18 K. The strong Rydberg progressions, which usually dominate the spectra in the gas phase, are found to completely disappear in the solid phase. In the absence of these transitions, the remaining broad bands centered at 4.3, 4.5, 6.2, 8.7, and 9.8 eV energy loss can be assigned to the 1 3A2(n→π*), 1 1A2(n→π*), 1 3A1(π→π*), 1 3B1(σ→π*), and 2 3A2(σ→π*) valence electronic transition of acetone, respectively. A broad feature ranging from 11 to 16 eV and having a maximum around 13.8 eV is ascribed to several overlapping autoionizing excited states. From a comparison with infrared and Raman spectra, the energy-loss peaks observed below 1 eV are found to be due to excitation of the fundamental, overtone, and combination vibrational modes of the molecule. Their incident energy dependence is showing broad vibrational enhancement maxima at 4, 7, and 9 eV, which are attributed to the formation of single-particle or shape resonances of 2B1, 2A1, and 2A2 (or 2B2) symmetries, respectively.

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Acetone photophysics in seeded supersonic molecular beams

Cited by 52 publications

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Photodynamics of Small Aliphatic Ketones in a Supersonic Jet Expansion

Photodynamics of Small Aliphatic Ketones in a Supersonic Jet Expansion

Ultrafast dissociation dynamics of acetone: A revisit to the S1 state and 3s Rydberg state

Low-energy electron-energy-loss spectroscopy of condensed acetone: Electronic transitions and resonance-enhanced vibrational excitations

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