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Little is known about the excited-state structures of most inorganic compounds. Time-resolved resonance Raman and time-resolved infrared spectroscopies can provide only indirect structural information for short-lived excited species in solution at room temperature. Time-resolved X-ray diffraction has the potential to give more direct information, but no excited-state structures have yet been reported; picosecond gas-phase electron diffraction has been proposed recently, but not yet demonstrated. Here we report a technique that combines the X-ray absorption fine-structure (XAFS) method with rapid-flow laser spectroscopy to measure structural changes in a solution-phase excited-state transition-metal complex with microsecond resolution. We find that the triplet excited state of Pt2(P2O5H2)4(4-), with a lifetime of about 4 microseconds, undergoes a contraction in the Pt-Pt distance of 0.52 +/- 0.13 A relative to the ground state. We anticipate that time-resolved XAFS will have broad applications in chemistry and biology.

The I.soft-x-ray emission spectra for Al and Si, and the E emission for graphite and diamond are analyzed, taking into account the efFects of multielectron transitions which produce a low-energy tail on the main band. Through an appropriate transformation on the initial states, it is shown that the Anal-state rule of Yon Barth and Grossman is a direct result of exchange. A "Pauli rigidity" forces the initial-state wave function to approach that of the Snal state, except near the Fermi energy. An assumption of random phases allows a formal solution that includes single-particle shakeup events to all orders. It is argued that a low-energy feature of silicon is structure due to the shakeup of single-particle-like excitations rather than a plasmon satellite.

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