CF3Br

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

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:

agust,heima,....Sept10/XLS-081210ak.xls

E(CF3+ + Br-) = 24035.31 + 72912.48 - 27129.17 = 69818.62197 cm-1

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

400

300

200

100

0

Rel

ativ

e In

tens

ity

84x1038280787674Energy (cm-1)

agust, heima,...PXP-291110ks/Leiðrétt-291110ks-081210ak.pxp

UV spectrum: 75493.46 cm-1 Vis spectrum: 75332.15 cm-1

CF3* + Br thresholds

500

400

300

200

100

0

828078767472x103

UV spectrum: 75493.46 cm-1 Vis spectrum: 75332.15 cm-1

CF3* + Br thresholds

agust,heima,... PXP-291110ks/Br 1D-REMPImW-291110ks-081210ak.pxp

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

100

90

80

70

60

50

40

30

20

10

0

x103

R(CF3 –Br)

CF3 + Br

CF3 + + Br

CF3Br(?)

CF3Br+ + e-

CF3 + + Br-

E/cm -1

ca. 24035.31 cm-1

96947.79 cm-191980 cm-1

69818.62 cm-1

80 000 cm-1

(Semi) schematic energy figure:

{CF3+Br-}?

Ion-pair state?

CF3 * + Br

75493.46/75332.15 cm-1

Agust,heima,...CF3Br/Sept10/PXP-081210ak.pxp; Layout::0, Graph: 0, Table::0

100

90

80

70

60

50

40

30

20

10

0

x103

R(CF3 –Br)

CF3 + Br

CF3 + + Br

CF3Br(?)

CF3Br+ + e-

CF3 + + Br-

E/cm -1

ca. 24035.31 cm-1

96947.79 cm-191980 cm-1

69818.62 cm-1

80 000 cm-1

Possible dissociation mechanism(1):Ry -> Ion-pair -> CF3+ + Br- formation

{CF3+Br-}?

Ion-pair state?

CF3 * + Br

75493.46/75332.15 cm-1

Agust,heima,...CF3Br/Sept10/PXP-081210ak.pxp; Layout::0, Graph: 0, Table::0

CF3 + + Br-

(1)

100

90

80

70

60

50

40

30

20

10

0

x103

R(CF3 –Br)

CF3 + Br

CF3 + + Br

CF3Br(?)

CF3Br+ + e-

CF3 + + Br-

E/cm -1

ca. 24035.31 cm-1

96947.79 cm-191980 cm-1

69818.62 cm-1

80 000 cm-1

Possible dissociation mechanism(2):Ry -> CF3* + Br dissociation

{CF3+Br-}?

Ion-pair state?

CF3 * + Br

75493.46/75332.15 cm-1

Agust,heima,...CF3Br/Sept10/PXP-081210ak.pxp; Layout::0, Graph: 0, Table::0

(2)

400

300

200

100

Rel

ativ

e In

tens

ity

75.8x10375.675.475.275.074.874.674.4Energy (cm-1)

CF3* + Br thresholds

UV spectrum: 75493.46 cm-1 Vis spectrum: 75332.15 cm-1

This brake in CF3+ intensity could bebecausea) -for 2hv < 75332 cm-1 only channels (1) occurs (i.e. CF3Br** ->-> CF3+ + Br-)b) for hv > 75332 cm-1, competitionBetween (1)(direct CF3+ formation) and (2)(CF3* formation)

However based on PD data the observedCF3+ signal all over most probably is mainly due to (1) (i.e. direct CF3+ formation)

agust, heima,...PXP-291110ks/Leiðrétt-291110ks-081210ak.pxp

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

600

400

200

0

Rel

ativ

e In

tens

ity

85x1038075Energy (cm-1)

Fluorescence maxima

(a) (b) (c) (d)

agust, heima,...PXP-291110ks/Leiðrétt-291110ks-081210ak.pxp

The fluorescenec maxima do not match CF3+ signal maxima. On the contraryIt 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)!

Try to search for systematic spacing between peaks close to 0.3 and 0.46 eV:

1) 11.4 eV

2) 11.7 eV

http://notendur.hi.is/agust/rannsoknir/papers/jcp101-2069-94.pdf :

Now let´s look at quantum defects:

500

400

300

200

100

0

Rel

ativ

e In

tens

ity

82x10380787674Energy (cm-1)

0.2 eV

0.3 eV

0.46 eV

0.264 eV 0.35 eV

1) En = 74546.9 cm-1 =9.24 eV

2) En = 9.24+0.3 =9.24 eVagust, heima,...PXP-291110ks/Leiðrétt-291110ks-081210ak.pxp

= n – sqrt(R/(EI-En)); n = 5, R = 13.61 eV

1) = 2.52) = 2.5

Which is what one might expect for 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) andhttp://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 and2) [CF3Br+ (X 2E1/2)]c 5p

Possibly the peak near 80500 cm-1 is due to transition to [CF3Br+ (A 2E1/2)]c 5p

...but what about the “peak” just below 77000 cm-1, i.e ca 1000 cm-1 aboveThe 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(?)