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Rotational energy transfer of optically centrifuged CO is investigated with high-resolution transient IR absorption probing and master equation modeling. Observed rates are smaller than simulated rates, highlighting the role of angular momentum in collisional relaxation.

The effect of CO rotational energy on bimolecular reactions to form electronically excited C2 is reported here. The reactions are initiated by CO multiphoton absorption of 800 nm light in strong optical fields using two different polarization configurations based on shaped chirped pulses. The observation of Swan band emission indicates that C2(d3Πg) is a reaction product. The optical polarization is in the form of either an optical centrifuge or a dynamic polarization grating. In each case, the strong field aligns CO molecules and induces multiphoton absorption. Power-dependent measurements indicate at least seven photons are absorbed by CO; CO(a3Π) is a likely reactant candidate based on kinetic modeling. Relative reaction efficiencies are determined by measuring Swan band emission intensities. For a CO pressure of 100 Torr and an optical intensity of I = 2.0 × 1013 W cm−2, the relative C2(d3Πg) yield with the dynamic polarization grating is twice that with the optical centrifuge. The extent of CO rotational energy was determined for both optical polarizations using high-resolution transient IR absorption for a number of CO states with J = 62–73 and Erot up to 10 400 cm−1. Optical centrifuge excitation generates at least 2.5 times more rotationally excited CO molecules per quantum state than the dynamic polarization grating. The results indicate that the effect of large amounts of CO rotational energy is to reduce the yield of the C2 products.

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.