ultraviolet photodissociation dynamics of the 3-cyclohexenyl radical michael lucas, yanlin liu,...

Ultraviolet Photodissociation Dynamics of the 3-Cyclohexenyl

Radical

Michael Lucas, Yanlin Liu, Jasmine Minor, Raquel Bryant, Jingsong Zhang

Department of Chemistry

University of California, Riverside

69th International Symposium on Molecular Spectroscopy

6/17/2014

Cyclohexyenl Radical

Cycloalkanes are important component of conventional fuels

Cyclohexane model cycloalkane Major producer of benzene

Previous Research: cyclohexyl, phenyl What effect does the double bond have on the

photochemistry?

0

10

20

30

40

50

60

70

0.0

47.14

62.25

47.0947.09

Ene

rgy

(kca

l/mol

)

+ H

+ H

+ H30.0

11.0

+ H

Potential Energy Diagram of c-C6H9

~~

●

●

●

K. Furukawa et al. Int. J. Chem. Kin. 6 (1974) 337NIST Chemistry WebBook

High-n Rydberg H-atom Time-of-Flight (HRTOF)

H

Lyman-a Probe

121.6 nm

Photolysis

Pulsed Valve

Rydberg Probe

366.2 nm

Detector

Skimmer

193

nm

H transitions

1

2

n H+

H (n)

H (22P)

121.6 nmLyman-a

366.2 nm

K. Welge and co-workers, J Chem Phys 92 (1990) 7027

3-chlorocyclohexene3-bromocyclohexene

H-atom TOF Spectra check precursors

244 nm

Inte

nsit

y (a

rb. u

nits

) 3-chlorocyclohexene244 nm

10 30 50 70 90 110 130 150

3-bromocyclohexene

Inte

nsit

y (a

rb. u

nits

)

Time of Flight (s)

H-atom Product Action Spectrum compare with absorption spectrum

R. Schuler et al. Chem. Phys. Lett. 27 (1974) 369; D. Pratt et al. J. Am. Chem. Soc. 96 (1974) 5588

220 230 240 250 260 270 280

This work Schuler et al. Pratt et al.

In

tens

ity (

arb.

uni

ts)

Wavelength (nm)

CM Product Translational Energy Distribution

0 10 20 30 40 50 60 70 80

P

(ET)

CM Translational Energy (kcal/mol)

+ H

+ H

+ H

250 nm

Average ET Release

230 235 240 245 250 255 260 2650.0

0.2

0.4

0.6

0.8

1.0

Ave

rage

f T

Wavelength (nm)

H-atom Product Angular DistributionE

v

q

0 20 40 60 80 100-1

0

1

2

Ani

sotr

opy

Para

met

er

Time of Flight (s)

244 nm

10 30 50 70 90 110 130 150

Inte

nsity

(ar

b. u

nits

)

Time of Flight (s)

= 0o

= 90o

244 nm

Major: β ~ 0Isotropic distributionDissociation time slower than 1 rotational period (ps)

Minor: β < 0Anisotropic distributionDissociation time faster than 1 rotational period

*

0

10

20

30

40

50

60

70

0.0

47.14

62.25

47.0947.09

Ene

rgy

(kca

l/mol

)

+ H

+ H

+ H30.0

11.0

+ H

Photodissociation Mechanism

~~

●

●

●

Repulsive dissociation

I.C. UnimolecularDissociation

Summary

UV photodissociation dynamics of cyclohexenyl was studied in 232-262 nm for the first time

Observed: cyclohexenyl → cyclohexadiene + H Modest translational energy release, fT ~ 0.15 Two components

Major: Isotropic distribution, β ~ 0 Dissociation mechanism: internal conversion from excited electronic state

followed by unimolecular dissociation on ground electronic state Minor:

Anisotropic distribution, β < 0 Dissociation mechanism: direct dissociation from excite state or repulsive part

of ground state

0 20 40 60 80 100

*

P(E

T)

CM Translational Energy (kcal/mol)

Cyclohexyl C

6H

9 Parallel

C6H

9 Perpendicular

*

Comparison With Cyclohexyl

Comparison With Cyclohexyl

230 235 240 245 250 255 260 2650.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

A

vera

ge f T

Wavelength (nm)

Cyclohexenyl Cyclohexyl

Comparison With Cyclohexyl

Moderate translational energy release

Two component Major

Isotropic distribution Statistical distribution Hot radical dissociation

mechanism

Minor Anisotropic distribution, β < 0 Repulsive dissociation mechanism

Large translational energy release

Anisotropic distribution, β > 0 Non-statistical distribution

Dissociation mechanism: direct dissociation from the excited state and/or on the repulsive part of the ground state (possibly via conical intersection).

Cyclohexenyl Cyclohexyl

Acknowledgements

Prof. Jingsong Zhang

Yanlin Liu

Jasmine Minor Raquel Bryant

Zhang Group