thomas j. preston, michael a. shaloski, and f. fleming crim infrared transient absorption...

Thomas J. Preston, Michael A. Shaloski, and F. Fleming Crim

Infrared Transient Absorption Spectroscopy of Bromoform Isomerization

Isomerization of Halomethanes

Preston et al. J. Chem. Phys. 2011, 135, 114503

Potential Energy Surface for Isomerization

Preston et al. J. Chem. Phys. 2011, 135, 114503

Bromoform Isomerization

Carrier et al. J. Phys. Chem. A. 2010, 114, 1548

Infrared Probing (Matrix Studies)

George et al. J. Chem. Phys. 2011, 135, 124503

ModeDescription

Transition Frequency in cm-1

CHBr3 C-H Stretch 3051

iso-CHBr2-Br C-H Stretch 3076

Infrared Probing (Time-Resolved)

Transition Frequency in cm-1

IR Bleach 3027

IR Absorbance 3052

Infrared Probing (Time-Resolved)

Feature  τ1  τ2

IR Bleach 5.3±2.6 22±7

IR Absorbance 9.0±0.6 98±17

443 nm Absorbance 19±1.0 124±44

Assignments

George et al. J. Chem. Phys. 2011, 135, 124503

Early Feature Assignment

Time-Dependent DFT

-M06-2x functional

-Sadlej-pVTZ basis set

Species l / nm e / M-1cm-1

Br--CHBr3 300 3860

Br--CHBr3 369 1535

CHBr3--Br--CHBr3 332 1185

CHBr3--Br--CHBr3 339 1355

Chromophore should be dependent on bromoform concentration

Dilution Study

Repeated 267 pump, 350 – 700 nm probe

-Varied concentration from 100% – 2% bromoform

-Normalized 1 ns signals

-Scaled 2 ps signal by same factor

Summary

IR ResultsPhotolysis leads to prompt bleach in

C-H region of bromoformAbsorption feature of iso-bromoform

appears with a characteristic time of 9.0 psLasts > 1 ns

UV/Visible Results490 feature assigned to isomer390 feature assigned to

Br – CHBr3 contact pairElectronic structure calc.Dilution experiment

Acknowledgements

NSF Funding Crim Group

Fleming CrimThomas J. Preston

CollaboratorsBob McMahonScott ReidNed Sibert