1. Dynamical “Fingerprinting” in Formaldehyde Dissociation Steven J. Rowling Scott H. Kable Sridhar A. Lahankar Arthur G. Suits

2. The Many Fates of Excited Formaldehyde H 2 CO(S 1 )H 2 CO(S 0 ) + h H 2 CO(S 1 )H 2 CO(S 0 *)CO + H 2 H 2 CO(S 1 )H 2 CO(S 0 *) [HCO—H]‡(S 0 *)CO + H 2 H 2 CO(S 1 )H 2 CO(S 0 *)HCO + H H 2 CO(S 1 )H 2 CO(T 1 *)HCO + H kfkf k IC k ISC

3. Measuring Product State Distributions H 2 CO Fluorescence HCO

4. Distributions from Low-Level Excitation 22412241 5 1 & 1 1 4 1 22612261 E avail = 330 cm  1 E avail = 865 cm  1 E avail = 869 cm  1 E avail = 1114 cm  1

5. Distributions from Higher Excitation 22612261 22432243 23412341 E avail = 1114 cm  1 E avail = 1482 cm  1 E avail = 1206 cm  1

6. Photofragment Excitation (Phofex) Probe Laser Excimer Dye Nd:YAG Nozzle MC Vac. gauge Pump Laser PMT Fluorescence HCO H 2 CO

7. Fingerprinting with Phofex Relative Population 0 510 15 N (E avail = 2640 cm  1 ) (E avail = 1242 cm  1 ) T 1 mechanism S 0 mechanism

8. Fingerprinting with Phofex Relative Population 0 510 15 N (E avail = 2640 cm  1 ) (E avail = 1242 cm  1 ) T 1 mechanism S 0 mechanism

9. At High Energy N = 0 N = 10 Energy (cm  1 ) 2 4 4 1 Band H 2 CO 22432243 24412441 Low N (S+T) E High N (S) T Dominant S Dominant Fluctuations Ground

10. Near T 1 Threshold N = 0 + 1 N = 10 + 12 Energy (cm  1 ) 2 2 4 3 Band H 2 CO 22432243 24412441 E T 1 Dominant S 0 Dominant Low N (S+T) High N (S) Ground Fluctuations

11. N = 0 + 1 N = 10 + 12 Energy (cm  1 ) 2 2 4 3 Band Near T 1 Threshold H 2 CO 22432243 24412441 E T 1 Dominant S 0 Dominant Low N (S+T) High N (S) Ground

12. N = 10 + 12 Energy (cm  1 ) 2 2 4 3 Band CO (J = 15) Indications from Other Channels H 2 CO 22432243 24412441 E T 1 Dominant S 0 Dominant Low N (S+T) High N (S)

13. Product Vibrational Excitation Energy (cm  1 ) v 3 = 0 v 3 = 1 2 2 4 3 Band H 2 CO 22432243 24412441 E T 1 Dominant S 0 Dominant No Vibration Vibrational Excitation Ground

14. Product Vibrational Excitation Energy (cm  1 ) H 2 CO 22432243 24412441 E T 1 Dominant S 0 Dominant No Vibration Vibrational Excitation Ground v 3 = 0 v 3 = 1 2 2 4 3 Band

15. Conclusions  “Fingerprint” technique can be used to qualitatively determine S 0 /T 1 branching ratios.  Near T 1 threshold, ISC is high for most, but not all, parent states.  Dominance of T 1 mechanism grows to become uniform at higher energies.  Both reaction channels produce vibrationally excited products, though the S 0 reaction slightly more so.

16. Remaining Questions & Future Work  Why do we see fluctuations near T 1 threshold?  How does tunneling through the T 1 barrier play a role?  Use D 2 CO to change state densities and tunneling probabilities.

17. Acknowledgements  Sydney Uni Laser Group Alan Maccarone Hong-Ming Yin Brianna Heazlewood Klaas Nauta  Suits Group of Wayne State  Sydney Uni Chemistry Machine Shop  Australian Research Council ($)