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CF3Br Bond Dissociation and CF3+ Formation Analysis

This document analyzes the bond dissociation and CF3+ formation in CF3Br using spectroscopic data and quantum defects. It revisits the threshold values and discusses the competition between direct CF3+ formation and CF3* formation. Additionally, it compares the fluorescence spectrum of CF3Br with the CF3+ signal maxima.

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CF3Br Bond Dissociation and CF3+ Formation Analysis

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  1. CF3Br agust,www,....cf3br/PPT-081210ak.ppt agust,heima,....Sept10/XLS-081210ak.xls agust, heima,...PXP-291110ks/Leiðrétt-291110ks-081210ak.pxp (CF3+) agust,heima,... PXP-291110ks/Br 1D-REMPImW-291110ks-081210ak.pxp (Br+)

  2. Bond dissociation for CF3Br revisited: The value used in http://notendur.hi.is/agust/rannsoknir/rempi/cf3br/PPT-090910ak.ppt (25 986.80 cm-1)is based on a paper from 1966 (see slide 3 in http://notendur.hi.is/agust/rannsoknir/rempi/cf3br/PPT-090910ak.ppt) The value used by Suto and Lee (JCP, 79(3), 1127, (´83) (see: http://notendur.hi.is/agust/rannsoknir/papers/jcp79-1127-83.pdf page 1131), based on Thermochemical data (Okabe, “Photochemistry of small molecules”, (1978)) is 2.98 eV (*8065.54093 cm-1/eV) = 24035.31 cm-1 which is is significantly lower. CF3+ + Br- threshold revisited: This affects the estimate of the CF3+ + Br- threshold: E(CF3+ + Br-) = 24035.31 + 72912.48 - 27129.17 = 69818.62197 cm-1 agust,heima,....Sept10/XLS-081210ak.xls

  3. CF3* + Br thresholds: Suto and Lee (JCP, 79(3), 1127, (´83) (see: http://notendur.hi.is/agust/rannsoknir/papers/jcp79-1127-83.pdf page 1132): UV spectrum: 6.38 + 2.98 eV =.... 75493.46 cm-1 Vis spectrum: 6.36 + 2.98 eV = ....75332.15 cm-1

  4. UV spectrum: 75493.46 cm-1 Vis spectrum: 75332.15 cm-1 CF3* + Br thresholds agust, heima,...PXP-291110ks/Leiðrétt-291110ks-081210ak.pxp

  5. CF3* + Br thresholds UV spectrum: 75493.46 cm-1 Vis spectrum: 75332.15 cm-1 agust,heima,... PXP-291110ks/Br 1D-REMPImW-291110ks-081210ak.pxp

  6. Now let´s look at the energetics with respect to CF3+ formation via CF3* formation (see fig. Next slide)

  7. (Semi) schematic energy figure: E/cm -1 CF3 + + Br 96947.79 cm-1 CF3Br+ + e- 91980 cm-1 CF3 * + Br 80 000 cm-1 75493.46/75332.15 cm-1 CF3 + + Br- 69818.62 cm-1 {CF3+Br-}? Ion-pair state? ca. 24035.31 cm-1 CF3 + Br CF3Br(?) R(CF3 –Br) Agust,heima,...CF3Br/Sept10/PXP-081210ak.pxp; Layout::0, Graph: 0, Table::0

  8. Possible dissociation mechanism(1): Ry -> Ion-pair -> CF3+ + Br- formation E/cm -1 CF3 + + Br 96947.79 cm-1 CF3Br+ + e- 91980 cm-1 (1) CF3 * + Br 80 000 cm-1 CF3 + + Br- 75493.46/75332.15 cm-1 CF3 + + Br- 69818.62 cm-1 {CF3+Br-}? Ion-pair state? ca. 24035.31 cm-1 CF3 + Br CF3Br(?) R(CF3 –Br) Agust,heima,...CF3Br/Sept10/PXP-081210ak.pxp; Layout::0, Graph: 0, Table::0

  9. Possible dissociation mechanism(2): Ry -> CF3* + Br dissociation E/cm -1 CF3 + + Br 96947.79 cm-1 CF3Br+ + e- 91980 cm-1 (2) CF3 * + Br 80 000 cm-1 75493.46/75332.15 cm-1 CF3 + + Br- 69818.62 cm-1 {CF3+Br-}? Ion-pair state? ca. 24035.31 cm-1 CF3 + Br CF3Br(?) R(CF3 –Br) Agust,heima,...CF3Br/Sept10/PXP-081210ak.pxp; Layout::0, Graph: 0, Table::0

  10. UV spectrum: 75493.46 cm-1 Vis spectrum: 75332.15 cm-1 • This brake in CF3+ intensity could be • because • -for 2hv < 75332 cm-1 only channels • occurs (i.e. CF3Br** ->-> CF3+ + Br-) • b) for hv > 75332 cm-1, competition • Between (1)(direct CF3+ formation) • and (2)(CF3* formation) • However based on PD data the observed • CF3+ signal all over most probably is • mainly due to (1) (i.e. direct CF3+ formation) CF3* + Br thresholds agust, heima,...PXP-291110ks/Leiðrétt-291110ks-081210ak.pxp

  11. Now let´s compare the “spin-orbit splitting” structure observed in the fluorescenec Spectrum for CF3Br and mentioned by Suto and Lee (JCP, 79(3), 1127, (´83) (see: http://notendur.hi.is/agust/rannsoknir/papers/jcp79-1127-83.pdf page 1132), i.e.

  12. Fluorescence maxima (b) (c) (a) (d) agust, heima,...PXP-291110ks/Leiðrétt-291110ks-081210ak.pxp

  13. The fluorescenec maxima do not match CF3+ signal maxima. On the contrary It looks more as if the maxima are in between peaks or close to minima in CF3+ signals (peaks (a)- (c). This could further indicate that there is a competition between channels (1) and (2)! http://notendur.hi.is/agust/rannsoknir/papers/jcp101-2069-94.pdf : 2) 11.7 eV 1) 11.4 eV Try to search for systematic spacing between peaks close to 0.3 and 0.46 eV:

  14. Now let´s look at quantum defects: 0.3 eV 0.46 eV 0.2 eV 0.35 eV 0.264 eV 1) En = 74546.9 cm-1 = 9.24 eV 2) En = 9.24+0.3 = 9.24 eV agust, heima,...PXP-291110ks/Leiðrétt-291110ks-081210ak.pxp

  15. = n – sqrt(R/(EI-En)); n = 5, R = 13.61 eV 1) d = 2.5 2) d = 2.5 Which is what one might expect for d for R-Br, p orbitals (and better value than that given by Eden et al. (http://notendur.hi.is/agust/rannsoknir/papers/cp323-313-06.pdf ) of 2.71) : See: http://notendur.hi.is/agust/rannsoknir/papers/jpcA112-7170-08.pdf (CH3Br) and http://notendur.hi.is/agust/rannsoknir/papers/CP148-315-90.pdf (Br2) Ergo: I conclude that the peaks at 1) just below 76000 cm-1 and 2) ca 78000 cm-1 are due to transitions to the Rydberg states: 1) [CF3Br+ (X 2E3/2)]c 5p and 2) [CF3Br+ (X 2E1/2)]c 5p Possibly the peak near 80500 cm-1 is due to transition to [CF3Br+ (A 2E1/2)]c 5p

  16. ...but what about the “peak” just below 77000 cm-1, i.e ca 1000 cm-1 above The peak for [CF3Br+ (X 2E3/2)]c 5p . Could that be a vibrational Band? NIST => ERGO: yes it could indeed be a vibrational band such as CF3 stretching(?)

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