J-Specific Dynamics in an Optical Centrifuge Matthew J. Murray, Qingnan Liu, Carlos Toro, Amy S. Mullin* Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 68 th Molecular Spectroscopy Symposium at the Ohio State University Funding: University of Maryland and National Science Foundation

Extreme Orientation of Molecules An optical centrifuge drives molecules to ultra-high rotational states with oriented angular momentum—a single M J. Compared to Keller, A., Control of the Molecular Alignment or Orientation by Laser Pulses. In Mathematical Horizons for Quantum Physics, 2010.

Operating Principles of the Optical Centrifuge A molecule with an anisotropic polarizability, , aligns with the electric field. During the optical centrifuge pulse, the electric field angularly accelerates from 0 to rad/sec. Interaction energy Karczmarek, J.; Wright, J.; Corkum, P.; Ivanov, M., Optical centrifuge for molecules. Phys. Rev. Lett. 1999, 82 (17),

Creating an Optical Centrifuge Two oppositely-chirped 800 nm pulses, each with opposite circular polarization Yuan, L. W.; Toro, C.; Bell, M.; Mullin, A. S., Spectroscopy of molecules in very high rotational states using an optical centrifuge. Faraday Discuss. 2011, 150, Create a linear electric field which angularly accelerates

Previous Optical Centrifuge Studies of CO 2 Transient IR absorption: appearance of J=76 followed by relaxation (10 Torr) Yuan, L. W.; Teitelbaum, S. W.; Robinson, A.; Mullin, A. S., Proc. Natl. Acad. Sci. U. S. A. 2011, 108 (17), “prompt” rise is pressure-dependent: collision-induced transient signals Detector Response

J-Specific Dynamics in the Optical Centrifuge 300 K distribution Goal: Study the dynamics of a broad range of rotational states after the optical centrifuge pulse excites a sample In this work we look at the dynamics of J=76, 54, 36, and 0.

Quantum-resolved Transient IR Absorption of CO 2 High-J Probing CO 2 (00 0 0, J) + IR → CO 2 (00 0 1, J±1) Low-J Probing CO 2 (00 0 0, J) + IR → CO 2 (10 0 1, J±1) CO 2 + Optical Centrifuge → CO 2 (00 0 0, J ≈ 220) CO 2 (00 0 0, J ≈ 220) + CO 2 (300 K) → CO 2 (00 0 0, J) + CO 2 (00 0 0, J’)

Optical Centrifuge and High Resolution Transient IR Spectrometer *Optical Parametric Oscillator Energy: 50 mJ/pulse Pulsewidth: 100 ps Beam waist: 26 µm Rep. Rate: 10 Hz OPO* λ~2.7 µm Diode Laser λ~4.3 µm

Assessment of Strong Field Phenomena Compare transient absorption for CO 2 J=76 with same total power (~35 mJ/pulse)

Transient Absorption Measurements of CO 2 J=54 and 76 J=54 J=76  ’ =290 ns  ’ =2.0  s  ” =21  s  ” =4.5  s Transient appearance then decay is seen for both states J=76 appearance is ~10x faster than J=54 Collision-induced decay of J=76 is ~5x faster than J=54

Doppler Broadened Transient Absorption Line Profile of J=76 τ 1 =170 ns τ 2 =7.2 µs 10 ns between collisions at 10 Torr Early Time Translational Temperatures Long Time Translational Temperatures

Doppler Broadened Transient Absorption Line Profile of J=54 Early Time Translational Temperatures Long Time Translational Temperatures

Time Dependent Temperatures and Populations for J=76 and J=54 τ A =1.3 µs τ R =31 µs Both J=76 and J=54 show molecules appear into these states with large translational energies. τ A =240 ns τ R =1.8 µs J=54 J=76 J=54

Transient Absorption Measurements of CO 2 J=36 Appearance in wingsDepletion at line center Raw Transient Smoothed Transient

Doppler Broadened Transient Absorption Line Profile of J=36 Appearance Depletion 20 ns between collisions at 5 Torr

Time Dependent Temperature and Population for CO 2 J=36 τ A =2.5 µs τ D =1.2 µs The rates at which population enters and leaves J=36 are only ~2x different. Molecules appear into J=36 with high translational energy and those that leave the state have low translational energy.

Transient Absorption of CO 2 J=0

Doppler Broadened Transient Line Profile of CO 2 J=0 Early Time Translational Temperatures Long Time Translational Temperatures τ=1.9 µs

Time Dependent Temperature and Population for J=0 τ D =1.25 µs τ R =110 µs We see molecules being depleted from J=0 and J=36 are from a slower subset of molecules in the initial 300 K ensemble. Population recovery of J=0 is relatively slow.

3-State Rotational Distribution Use appearance population from J=76, 54, and 36. T rot Decay ~32 Collisions

Quasi-Equilibrium at 550 K J=54 J=0 Conservation of energy indicates that ~2% of CO 2 molecules are initially excited by the optical centrifuge to J ~220

Summary  We have used high resolution transient IR absorption to investigate the J-dependent behavior in an optical centrifuge.  We see evidence for fast translational energy gain followed by relaxation due to collisions in the optical centrifuge.  Results show evidence for long-lived energy content in molecules.  J-dependent profiles show the rotation to rotation- translation energy transfer process through a collisional cascade. The CO 2 molecules reach a quasi-equilibrium temperature of ~550 K.

Quasi-Equilibrium at 550 K J=54 J=0 E rot = Centrifuge-Induced Rotational Energy N J = Number Density of Centrifuged Molecules N tot = Total number density in cell T i = 300 K T f ≈ 550 K

Depletion Transient Absorption from Low J