1. Brookhaven Science Associates U.S. Department of Energy Hot band transitions in CH 2 Kaori Kobayashi *, Trevor Sears, Greg Hall Department of Chemistry Brookhaven National Laboratory Thanks to: Prof. Hideto Kanamori, Tokyo Institute of Technology Funding: DOE Division of Chemical Sciences, Office of Basic Energy Sciences * Current address, Dept. of Physics, Toyama University

2. Brookhaven Science Associates U.S. Department of Energy Outline Near-IR spectrum of CH 2 –Renner-Teller states a, b –Spectra involving levels near b-state origin Transitions from a(010) –Rotational structure within this level –Perturbing triplet state (X) levels Observation of c-state of CH 2

3. Brookhaven Science Associates U.S. Department of Energy Electronic states of CH 2 (a) (X) (b)

4. Brookhaven Science Associates U.S. Department of Energy Near-IR spectrum of CH 2 Two singlet states-correlate with a 1 Δ state at linearity Transitions between them result in band system in near-IR and visible Perturbations due to mutual interactions (RTE) and background of triplet (X) state levels Cuts through the lowest three electronic PES’s along bending coordinate

5. Brookhaven Science Associates U.S. Department of Energy Time-resolved FM absorption CH 2 CO + 308nm → CH 2 + CO Ti:sapphire laser replaced by tunable diode operating near 1.3 microns Shot noise sensitivity Sub-microsec. time resolution, Doppler- limited frequency resolution

6. Brookhaven Science Associates U.S. Department of Energy Transitions near 7400 cm -1 Below the b-a band origin, only hot bands or overtone transitions –Access region close to linearity from a(010) Ortho and para CH 2 3:1 intensity ratio easy to see here Spectra relatively uncomplicated, compared to shorter wavelengths

7. Brookhaven Science Associates U.S. Department of Energy Observed and calculated levels Also (0,10,0) 2

8. Brookhaven Science Associates U.S. Department of Energy ã(0,1,0) state rotational levels Accumulated combination differences for ã(0,1,0) obtained from multiple bands as follows: b(0,0,0) K = 2 b(0,2,0) K = 0, 1, 2, 4 a(0,7,0) K = 1 a(0,10,0) K = 1, 3

9. Brookhaven Science Associates U.S. Department of Energy Fit ã(010) combination differences

10. Brookhaven Science Associates U.S. Department of Energy K=1 levels perturbed

11. Brookhaven Science Associates U.S. Department of Energy Perturbing levels? (vibronic origins) K a = 1 K a = 2K a = 0K a = 3K a = 4 1 CH 2 (0,1,0) 3 CH 2 (0,4,0) 3 CH 2 (0,3,0) 3 CH 2 (1,1,0) 3 CH 2 (0,1,1) 3 CH 2 (0,0,1) 3 CH 2 (1,1,0)

12. Brookhaven Science Associates U.S. Department of Energy Rotational levels K=1 a(010) K=1 X(040) K=3 X(030) K=2 X(011) 2 3 4 6 3 4 5 6 7 2 3 4 5 Observed

13. Brookhaven Science Associates U.S. Department of Energy CH 2 c-state Dominant electron configurations, wavefunctions contain both –“Forbidden” c-a transition OODR experiment (c) (a)

14. Brookhaven Science Associates U.S. Department of Energy OODR Spectra Pump b-a transition with ns dye laser approx 0.4 microsec after photolysis pulse. Record absorption of FM’d Ti:sapphire laser.

15. Brookhaven Science Associates U.S. Department of Energy c-state assignments Rotational levels in (0,11,0) of c 1 A 1 –All K=1 levels accessible from an ambient temperature sample of a 1 A 1 CH 2 –Some strong localized perturbations OODR technique applicable to search for other higher CH 2 electronic states –Particularly d 1 A 2 that is predicted to have a very small bond angle

16. Brookhaven Science Associates U.S. Department of Energy Finally Greg Hall and Anatoly Komissarov … and other members of the GPMD group at BNL Additional people who contributed to the work…. Yangsoo Kim