S M. Arrivo

Picosecond transient backward stimulated Raman scattering and pumping of femtosecond dye lasers

Abstract We report studies of transient, backward stimulated, Raman scattering (TBSRS) in solvents with a 10 Hz, 27 ps, 532 nm pump laser. The TBSRS effect was used to create pulses at 545 nm and 630 nm with durations of 2–3 ps and 5–10 μJ of energy. The duration, energy and fluctuations of the Raman pulse were studied as a function of pump energy and focal parameters. A 5 μJ Raman pulse was amplified in either a Raman amplifier or two stage dye amplifier to 1 mJ levels. A 545 nm pulse of 3 ps duration was generated in CCl 4 and was then used to pump a short cavity dye laser (SCDL). The SCDL oscillator and a 5 stage dye amplifier provided a pulse of 700 fs and 400 μJ that was tunable near 590 nm.

Infrared Spectral Hole Burning of 1:1 Hydrogen-Bonded Complexes in Solution

Transient picosecond infrared (IR) spectra of the OH and NH-stretch (v=0–1) absorption bands of several hydrogen-bonded complexes have been investigated. Solutions of 1:1 complexes of weak acids (methanol, triethylsilanol and pyrrole, < 0.1 mol/dm3) and bases (acetonitrile, pyridine and tetrahydrofuran, < 2 mol/dm3) in CCl4 at 295 K were interrogated with IR excitation and broadband probing. Lorentzian-shaped absorption bands are uniformly bleached while those with near-Gaussian bandshapes produce transient spectral holes. These results indicate a base functionality and hydrogen-bond strength dependence for determining the broadening mechanisms of these absorptions.

Picosecond transient-IR absorption of unsaturated transition metal complexes

We report transient infrared spectra for the addition of perfluoroheptane to Cr(C0)5 which is created by the ultraviolet photodissociation of Cr(C0)6 in liquid perfluoroheptane. We compare both 266 nm and 297 nm excitation wavelengths and demonstrate that two product vibration bands at 1971 and 1938 cm1 are forming with a nominal 60 p5 rate constant, while fast rising and slowly decaying (80-220 ps) transients have absorption over the 1920-1983 cm1 range. These transient absorption features are assigned to Cr(C0)5 with vibrational quanta of 0,1,2 which are broadened from geometric distortions. These features decay from reaction, vibrational relaxation of GO, and vibrational relaxation of low frequency vibrational modes.

Picosecond infrared study of vibrational-dependent electron transfer rates

Photoinduced electron transfer and thermal back electron transfer in the inorganic donor- acceptor contact ion-pair {Cp2Co+Co(CO)4-} have been observed in solution with picosecond time-resolved infrared absorption spectroscopy. Optical excitation of a charge transfer band created by cobalt interaction causes an immediate electron transfer to form a neutral pair, and the spontaneous return electron transfer is followed by monitoring the CO stretching frequencies of the Co(CO)4- and Co(CO)4 molecules. We have observed the back electron transfer decay for up to 3 quanta of the CO stretching mode in the neutral pair for dichloromethane solvent. The arrival kinetics into the ion pair and ion pair vibrational relaxation rates for final return to the vibrationless level have been studied for up to 4 quanta of vibration. These are the first measurements of an electron transfer process with vibrational resolution, and comparison to models is in progress.