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Multi-photon UV photolysis of gaseous polycyclic aromatic hydrocarbons: Extinction spectra and dynamics
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10.1063/1.4816003
/content/aip/journal/jcp/139/5/10.1063/1.4816003
http://aip.metastore.ingenta.com/content/aip/journal/jcp/139/5/10.1063/1.4816003

Figures

Image of FIG. 1.
FIG. 1.

Extinction coefficient at 650 nm as a function of time. (a) Example of type I dynamic behavior. Arrows indicate the excitation of the gas mixtures with n (=1…10) focused UV pulses. ∼ 24 mJ. (b) Example of type II dynamic behavior. The arrow indicates the time of excitation with 20 focused UV pulses; ∼ 18 mJ. (c) Example of type III dynamic behavior. The arrow indicates the time of excitation with 10 focused UV pulses. ∼ 10 mJ. Respective buffer gases and pressures are stated in the panel. UV repetition rate 10 Hz.

Image of FIG. 2.
FIG. 2.

Resonance-enhanced -photon absorption processes of (a) naphthalene (left) and (b) biphenylene (right) upon excitation at 32 468 cm (308 nm), illustrated in two schematic Jabłoński diagrams. The energies of the 1- to 4-photon processes in the singlet manifold are indicated by horizontal dashed blue lines with the corresponding values on the right. IP = ionization potential.

Image of FIG. 3.
FIG. 3.

(a) Experimental schematic (top elevation). AL: achromatic lens, M: aluminium mirrors, W: fused silica windows, CM: (high reflectivity) cavity mirrors, JM: Joule (energy) meter. (b) Side elevation: Schematic of the six-way cross center piece ( ∼ 3.8 dm) of the static unstirred gas chamber ( ∼ 5.3 dm).

Image of FIG. 4.
FIG. 4.

(a) Sample mono-exponential decay behavior at 650 nm (dots) measured using the CRD setup; fit of mono-exponential function to data (red line) and the corresponding residuals. Fit parameters: decay time 4.7 s, max height 11.4 × 10 s, offset 7.5 × 10 s. Conditions: Excitation of naphthalene in 57.2 mbar of helium with 30 pulses at 20 Hz ( ≈ 25 mJ). (b) Sample growth and decay behavior at 650 nm (dots) measured using the IBBCEAS setup; fit of Gaussian function to data (blue line) and the corresponding residuals. Fit parameters: center time 6.3 s, FWHM 3.9 s, loss amplitude 0.0043, loss offset 8.6 × 10. Conditions: Excitation of naphthalene in 5.9 mbar of helium with 120 pulses at 50 Hz ( ≈ 24 mJ).

Image of FIG. 5.
FIG. 5.

(a) The first 75 min of time-dependent loss per pass at 550 nm. 500 pulses at 10 Hz with an average energy of 12.7 mJ began excitation of naphthalene, in 102 mbar of helium, at zero min. (b) Loss per pass spectra in the 390–620 nm region, A–D, as measured at times marked in panel (a). The lack of isolated features suggests that the source of loss is likely to be due to particles.

Image of FIG. 6.
FIG. 6.

(a) Time-dependent loss per pass at 650 nm. 25 pulses at 10 Hz with an average energy of 78.9 mJ began excitation of naphthalene, in 107 mbar of helium, at zero min. (b) Loss per pass spectra in the 550–850 nm region, A–D, as measured at times marked in panel (a). The lack of isolated features suggests that the source of loss is likely to be due to particles.

Image of FIG. 7.
FIG. 7.

Sample time-dependent loss per pass at 550 nm, panel (a1), and 650 nm, panel (a2), for biphenylene buffered with ∼80 mbar of helium. 100 UV pulses at 5 Hz began excitation of biphenylene, at 0 min in both measurements. The average pulse energies for (a1) and (a2) were 18.2 and 96 mJ. Panels (b1) and (b2) show loss per pass spectra in regions (a) and (b), measured at times marked in panels (a1) and (a2). The lack of isolated features suggests that the source of loss is likely to be due to particles, similar to naphthalene mixtures following photolysis.

Image of FIG. 8.
FIG. 8.

(a) Sample time-dependent behavior of optical losses at 650 nm measured using the CRD setup and the effect of stirring the gas mixture, at ∼23 min, on the behavior. The optical loss falls immediately after stirring begins, but it then increases slightly before returning back to the baseline optical loss level. No further change in optical loss occurs following the initial slight increase. Conditions: Excitation of naphthalene in 100.5 mbar of helium with 10 pulses at 10 Hz ( ≈ 24 mJ). (b) The inset shows an enlargement of the dashed time regime when stirring commenced.

Image of FIG. 9.
FIG. 9.

(a) Time-dependent loss per pass at 650 nm after excitation of naphthalene in 96 mbar of helium with 2000 UV pulses at 10 Hz with an average energy of 8.2 mJ. The broadband spectra recorded at the times marked A…F are shown in the three lower panels. (b) Loss per pass spectra at times A and B. (c) Loss per pass spectra at times C and D. (d) Loss per pass spectra at times E and F. Each pair of spectra A and B, C and D, E and F have the same loss per pass at 650 nm as indicated by horizontal lines in panel (a).

Tables

Generic image for table
Table I.

Summary of appearance energies of naphthalene fragments.

Generic image for table
Table II.

Summary of appearance energies of biphenylene fragments.

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/content/aip/journal/jcp/139/5/10.1063/1.4816003
2013-08-05
2014-04-24
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Multi-photon UV photolysis of gaseous polycyclic aromatic hydrocarbons: Extinction spectra and dynamics
http://aip.metastore.ingenta.com/content/aip/journal/jcp/139/5/10.1063/1.4816003
10.1063/1.4816003
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