1. The Origin Band of the b – a System of CH 2 Gregory Hall, and Trevor Sears Department of Chemistry Brookhaven National Laboratory Bor-Chen Chang Department of Chemistry National Central University, Taiwan Zhong Wang Department of Math and Science, Eastern Campus Suffolk County Community College, SUNY Ju Xin Department of Physics and Engineering Technology Bloomsburg University

2. Methylene (CH 2 ): the simplest carbene Two singlet states are degenerate at linearity. Transitions between them result in an electronic spectrum from near-IR through visible. Isolated levels are perturbed by nearly degenerate triplet state levels H H 1B11B1 3B13B1 H H 1A11A1 H H Energy / cm -1  0.0 -0.5 0.5 1.0 1.5 2.0 2.5 3.0 Degrees X (Triplet) a (Singlet) b (Singlet) Energy / ×10 4 cm -1

3. Detailed Optical-Optical Double Resonance setup FM Transient Absorption Spectrometer EOM: electro-optic modulator; RF: radio frequency; IF: intermediate frequency; LO: local oscillator; LP: low-pass filter; HP: high-pass filter; BS: beam splitter; SA: spectral analyzer; AP: amplifier.

4. An example of the observed data The probe Monitors b(0,3,0)-a(0,0,0) 3 03 – 3 13 at 12205.073 cm -1. Double resonance signal is seen when the pump wavelength is resonant with a transition in the b(0,0,0)- a(0,0,0) band originating in the probed lower state level. OPO idler wavenumber/cm -1 Intensity (mV) Time ( X 0.2 μs)Intensity / arb. unit Scan OPO idler wavelength near 1.2 microns a b'b' b

5. -8.048374.288366.243 13 - 3 03 -5.418377.448372.032 12 - 2 02 -7.758381.108373.351 11 - 1 01 -8.018340.408332.395 05 - 5 15 -6.288340.128333.944 04 - 4 14 -5.168340.378335.213 03 - 3 13 -4.238341.398337.162 02 - 2 12 obs. - calc. cm -1 Calculated*/ cm -1 Observed/ cm -1 b(000) - a(000) J' KaKc – J" KaKc Transitions from Double Resonance Experiment * from Gu et al J. Mol. Struct. 517-8, 247 (2000), and P. Jensen

6. Absorption spectrum (170 cm -1 section) obtained by scanning extended cavity diode laser running near 1.2 microns (8500 cm -1 ) (614 measurable lines). -240 -200 -160 -120 -80 -40 0 40 K=0 ← K=1 sub-band origin with J-assignments

7. Assigned Rotational Lines a (49 lines) …… a All assigned transitions originate from the ã (0, 0, 0) level. b Experimental error limit is 0.007 cm-1. c Jensen, private communication (borrowed from other bands) d Confirmed by double resonance experiments.

8. Molecular parameters for the upper levels (cm -1 ) a,b. a One standard deviation limit in parentheses. b K a = 0 and K a = 1 lines are fitted separately, 42 unperturbed lines are included in the fit. Current work: Double resonance experiments to confirm some assignments

9. Some remaining mysteries: 1. The apparent strength of the spectrum is much larger than anticipated. 2. There are far more absorption lines than expected. - Must be seeing vibrational overtone and combination bands of the a-state. Stretching potential more anharmonic than believed?

10. Work at Brookhaven National Laboratory was carried out under Contract No. DE- AC02-98CH10886 with the U.S. Department of Energy. Dr. Ju Xin was supported by the Faculty and Student Teams program of the Educational Programs Department at Brookhaven National Laboratory. Acknowledgment