We have constructed an optical centrifuge with a pulse energy that is more than 2 orders of magnitude larger than previously reported instruments. This high pulse energy enables us to create large enough number densities of molecules in extreme rotational states to perform high-resolution state-resolved transient IR absorption measurements. Here we report the first studies of energy transfer dynamics involving molecules in extreme rotational states. In these studies, the optical centrifuge drives CO 2 molecules into states with J ∼ 220 and we use transient IR probing to monitor the subsequent rotational, translational, and vibrational energy flow dynamics. The results reported here provide the first molecular insights into the relaxation of molecules with rotational energy that is comparable to that of a chemical bond.carbon dioxide | rotational dynamics | transient spectroscopy | high-energy molecules | strong optical fields C ontrol of molecular energy for use in chemical and physical transformations requires tools for exciting specific degrees of freedom in molecules. A number of methods exist for preparing molecules with large, well-defined, and controllable amounts of energy in electronic, translational, and vibrational degrees of freedom, but until recently, it has been much more difficult to exert control over the rotational energy of molecules (1-14). Traditional methods for optically preparing rotationally hot molecules are limited by strict selection rules that constrain angular momentum changes to small values (15, 16). Microwave spectroscopy has been used to a limited degree for walking molecules up a rotational ladder, but only small amounts of rotational energy (ΔJ ∼ 5) could be imparted to molecules with this approach (17, 18). Static electric fields have been explored for orienting molecules, but this approach is impractical for rotating molecules into high-energy states due to the high angular velocity and voltages required (19). Rotational motion in molecules can be induced with strong optical fields leading to rotational recurrences, but the amount of rotational energy obtained with this method is fairly modest (19)(20)(21)(22)(23)(24)(25). In some cases, photochemical reactions and inelastic collisions can be used to produce rotationally hot molecules, but the products generally have broad and poorly controlled rotational energy distributions (26).An important development in the area of light-matter interactions is the optical centrifuge for molecules (27,28). In this device, powerful ultrafast chirped laser pulses deposit rotational excitation in molecules that is comparable to, and in some cases even exceeds, interatomic binding energies. The optical centrifuge was proposed by Corkum and coworkers in 1999 and was first demonstrated in 2000 (27, 28). They used an optical centrifuge to spin Cl 2 molecules into J ∼ 420 and used a time-of-flight mass spectrometer to detect Cl radicals that resulted from rotationally induced dissociation. The dissociation energy of Cl 2 is 3.5 eV, but rotational...

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The reactions of metastable diacetylene with benzene and toluene are explored using a molecular beam pumpprobe time-of-flight mass spectrometer. Diacetylene is laser-excited to the 2 1 0 6 1 0 band of the 1 ∆ u r X 1 Σ + g transition, whereupon rapid intersystem crossing occurs to the lowest triplet states. The triplet state diacetylene then reacts with either benzene or toluene as the gas mixture traverses a short reaction tube (∼20 µs). The reactions are quenched as the gas mixture expands into the ion source region of a time-of-flight mass spectrometer where the primary photoproducts are detected using vacuum ultraviolet (VUV) photoionization or resonant two-photon ionization (R2PI). The major products from the reaction of diacetylene and benzene have molecular formulas C 8 H 6 and C 10 H 6 , and are identified as phenylacetylene and phenyldiacetylene using R2PI spectroscopy. The major products from metastable diacetylene's reaction with toluene are C 9 H 8 and C 11 H 8 . The C 9 H 8 product is confirmed as a mixture of o-, m-, and p-ethynyltoluene, with the ortho product dominating. Mechanisms for the formation of the above products are proposed based on deuterium substitution studies of the reactions. The potential importance of these reactions is discussed as they relate to hydrocarbon growth in sooting flames. † Part of the special issue "C. Bradley Moore Festschrift".

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The reaction of metastable diacetylene with styrene is explored using a molecular beam pump−probe time-of-flight (TOF) mass spectrometer. Diacetylene is laser-excited to the 2 061 0 band of the 1Δu ← X1Σ+ g transition, whereupon rapid intersystem crossing occurs to the lowest triplet states. The triplet state diacetylene then reacts with styrene as the gas mixture traverses a short reaction tube (∼20 μs). The reaction is quenched as the gas mixture expands into a vacuum where the primary photoproducts are probed using vacuum ultraviolet (VUV) photoionization, resonant two-photon ionization (R2PI), and UV−UV holeburning. The major products from the reaction have molecular formulas C10H8, C12H8, and C12H9. Two different C10H8 products have been identified as 1-phenyl-1-buten-3-yne and m-ethynyl styrene using UV−UV holeburning and comparing with spectra of authentic samples. Mechanisms for the formation of the above products are proposed on the basis of deuterium substitution studies of the reaction. The potential implications of these reactions for the formation of polycyclic aromatic hydrocarbons in sooting flames is discussed.