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...
Combinational modulations of phase engineering and heteroatom doping are realized to prepare Fe-doped marcasite NiSe2 nanodendrites, which serve as a superior OER electrocatalyst with improved conductivity and excellent catalytic activity.
We have developed a high power optical centrifuge for measuring the spectroscopy of molecules in extreme rotational states. The optical centrifuge has a pulse energy that is more than 2 orders of magnitude greater than in earlier instruments. The large pulse energy allows us to drive substantial number densities of molecules to extreme rotational states in order to measure new spectroscopic transitions that are not accessible with traditional methods. Here we demonstrate the use of the optical centrifuge for measuring IR transitions of N2O from states that have been inaccessible until now. In these studies, the optical centrifuge drives N2O molecules into states with J ~ 200 and we use high resolution transient IR probing to measure the appearance of population in states with J = 93-99 that result from collisional cooling of the centrifuged molecules. High resolution Doppler broadened line profile measurements yield information about the rotational and translational energy distributions in the optical centrifuge.
The outcome of energy transfer due to single collisions between highly vibrationally excited pyrazine (E = 37,900 cm(-1)) and DCl is measured for the appearance of individual low-J rotational states of DCl using high-resolution transient IR absorption. Appearance profiles from double-Gaussian transient lineshapes were measured for a number of DCl states with J = 2-12. These data give information on the recoil velocity distributions, appearance rates, and populations of individual states of the scattered molecules. These data complement previous studies on high-J state DCl scattering (Li, Z.; Korobkova, E.; Werner, K.; Shum, L.; Mullin, A. S. J. Chem. Phys. 2005, 123, 174306), and together, they provide a full description of the V-RT collisions with DCl that quench pyrazine(E). Scattered DCl (v = 0) molecules with J = 2-21 are rotationally hot with T(rot) = 880 +/- 100 K. Center-of-mass translational energy distributions are T(rel) approximately 700 K for J < 15. Broader velocity distributions are observed for the J = 15-20 states. The rate constant for V-RT energy transfer is 4.6 x 10(-10) cm(3) molecule(-1) s(-1). This value is a lower limit to the overall rate constant for energy transfer and corresponds to approximately 85% of the Lennard-Jones collision rate. We estimate scattering into the DCl (v = 1) state occurs in approximately 1% of collisions. The energy transfer probability distribution P(DeltaE) is presented and yields DeltaE = 888 cm(-1).
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