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Molecular elimination of Br2 in photodissociation of CH2BrC(O)Br at 248 nm using cavity ring-down absorption spectroscopy
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10.1063/1.4767346
/content/aip/journal/jcp/137/21/10.1063/1.4767346
http://aip.metastore.ingenta.com/content/aip/journal/jcp/137/21/10.1063/1.4767346

Figures

Image of FIG. 1.
FIG. 1.

A portion of Br2 spectra acquired in the photolysis of CH2BrC(O)Br at 248 nm. (a) The pure Br2 spectrum containing the v = 0 band, (b) trace acquired experimentally, (c) spectral simulation taking into account all the isotopic variants of 79Br2, 79,81Br2, and 81Br2, and (d) the background spectrum obtained without irradiation of 248 nm. Partial assignments are added.

Image of FIG. 2.
FIG. 2.

A portion of Br2 spectra acquired in the photolysis of CH2BrC(O)Br at 248 nm. (a) Trace acquired experimentally for the bands of v = 0 and 1, (b) the simulated counterpart with the population ratio of Br2(v = 1)/Br2(v = 0) optimized at 0.5, (c) simulated counterpart with the transition involving only v = 0, and (d) simulated counterpart with the transition involving only v = 1.

Image of FIG. 3.
FIG. 3.

A portion of Br2 spectra acquired in the photolysis of CH2BrC(O)Br at 248 nm. (a) Trace acquired experimentally for the bands of v = 0, 1, and 2, (b) the simulated counterpart with the population ratio of Br2(v = 1)/Br2(v = 0) fixed at 0.5 and Br2(v = 2)/Br2(v = 0) adjusted to 0.2, (c) simulated counterpart with the transition involving only v = 0, (d) simulated counterpart with the transition involving only v = 1, and (e) simulated counterpart with the transition involving only v = 2.

Image of FIG. 4.
FIG. 4.

Laser energy dependence of Br2 fragment intensity at 519.68 nm contributed mainly from the rotational line P(37) of the (35,0) band.

Image of FIG. 5.
FIG. 5.

Br2 fragment intensity as a function of CH2BrC(O)Br pressure varied from 30 to 130 mTorr. The rotational line at 519.68 nm is selected for the measurements.

Image of FIG. 6.
FIG. 6.

(a) The Br2 spectra obtained in photodissociation of CH2BrC(O)Br at 100 mTorr and 30 ns photolysis-probe delay time. (b) The trace obtained in photodissociation of CH3C(O)Br at 248 nm with the same laser energy as used in (a), whereas the pressure was increased to 1000 mTorr with the same delay time, and (c) the trace obtained in CH3C(O)Br with the probe laser alone.

Image of FIG. 7.
FIG. 7.

Stern-Volmer plot of the reciprocal of excited state lifetime for CH2BrC(O)Br as a function of its pressure. Time-resolved laser-induced fluorescence was used to probe the lifetime upon irradiation at 248 nm.

Image of FIG. 8.
FIG. 8.

The dissociation pathways of CH2BrC(O)Br, in which the energies in units of kJ/mol relative to the ground state are computed with CCSD(T)/cc-pVTZ level of theory with B3LYP/cc-pVTZ zero-point energy corrections at B3LYP/cc-pVTZ optimized geometries.

Image of FIG. 9.
FIG. 9.

The related structures along the dissociation pathway of CH2BrC(O)Br.

Image of FIG. 10.
FIG. 10.

Temperature dependence of the Br2 line intensity at 519.68 nm in photodissociation of CH2BrC(O)Br at 248 nm. Photolysis laser energy was fixed at 19 mJ and sample pressure was at 150 mTorr.

Image of FIG. 11.
FIG. 11.

(A) (a) A portion of Br2 spectra acquired in the photolysis of CH2BrC(O)Br at 248 nm, (b) the Br2 spectra in the same range acquired in photolysis of CH3CHBrC(O)Br at 248 nm under otherwise identical condition, and (c) trace obtained for CH3CHBrC(O)Br with the probe laser alone. (B) (a) A portion of Br2 spectra acquired in the photolysis of CH2BrC(O)Br at 248 nm. (b) The Br2 spectra in the same range acquired in photolysis of (CH3)2CBrC(O)Br at 248 nm under otherwise identical condition, and (c) trace obtained for (CH3)2CBrC(O)Br with the probe laser alone.

Tables

Generic image for table
Table I.

The calculated energies for the B3LYP/cc-pVTZ optimized geometries of reactants(bromoacetyl bromide), intermediates, transition states, and dissociation products for the H, CO, H2, HBr, Br2, BrCO, H2O dissociation channels on the adiabatic singlet ground state potential energy surface of bromoacetyl bromide (CH2BrC(O)Br).

Generic image for table
Table II.

RRKM rate constants (s−1) computed with B3LYP/cc-pVTZ zero-point energy corrected CCSD(T)/cc-pVTZ energies, and B3LYP/cc-pVTZ harmonic frequencies for reactions paths on the adiabatic singlet ground state surface of CH2BrC(O)Br at 248 nm.

Generic image for table
Table III.

Comparison of number of states, density of states, and rate constants to produce Br2 among CH2BrC(O)Br, CH3CHBrC(O)Br, and (CH3)2CBrC(O)Br.

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2012-12-04
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Molecular elimination of Br2 in photodissociation of CH2BrC(O)Br at 248 nm using cavity ring-down absorption spectroscopy
http://aip.metastore.ingenta.com/content/aip/journal/jcp/137/21/10.1063/1.4767346
10.1063/1.4767346
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