T P. Dougherty

Ultrafast transient infrared absorption studies of M(CO)6 (M Cr, Mo or W) photoproducts in n-hexane solution

Abstract Following UV excitation, M(CO) 6 (Mue5fbCr, Mo or W) species in solution lose one CO ligand, and a solvent molecule occupies the vacant site. These photochemical reactions are studied using a transient broadband IR absorption technique with 390 fs time resolution. The progress of these reactions, including loss of the M(CO) 6 reactant, appearance of a solvated M(CO) 5 ( n -hexane) product and vibrational energy distribution and relaxation of the product, is monitored through changes in infrared absorption by the CO ligands near 2000 cm −1 .

Ultrafast infrared spectroscopy of vibrational CO-stretch up-pumping and relaxation dynamics of W(CO)6

Abstract The ultrafast infrared (IR) vibrational up-pumping and energy relaxation dynamics are reported of the T 1u CO-stretching manifold of W(CO) 6 in room temperature n -hexane solution. The frequency and energy content of the tunable 2 ps IR pump pulse strongly influences the distribution of vibrational level population. With broadband transient IR absorption spectroscopy, vibrational T 1 lifetimes of the overtone states of W(CO) 6 were directly determined to be 140 ± 20 (1 σ ) ps for ν = 1, 75 ± 20 ps for ν = 2 and 30 ± 15 ps for ν = 3. T 1u to E g intermode energy transfer occurs on the 10–20 ps timescale.

Transient infrared spectroscopy of (η5−C5 H5)Co(CO)2 photoproduct reactions in hydrocarbon solutions

Ultrafast photochemistry of CpCo(CO)2 in n‐hexane, 1‐hexene, and solvent mixtures (298 K) are reported. Multichannel infrared spectra (0.4 ps, 4 cm−1 resolution) identify the vibrational cooling of CpCo(CO)(n‐hexane) and CpCo(CO)(1‐hexene). The conversion rate of transient n‐hexane species to stable 1‐hexene product for 0.2–2.0 mol/liter 1‐hexene/n‐hexane solutions (k=1.4±0.2×1010 M−1u2009s−1) was determined.

Vibrational energy redistribution in Cp*Ir(CO)2 (Cp*=η5-pentamethylcyclopentadienyl) studied by broadband transient infrared spectroscopy

Picosecond vibrational energy dynamics involving the symmetric (2020 cm−1 and asymmetric (1953 cm−1) CO-stretching modes of Cp*Ir(CO)2 in room temperature n-hexane is measured using mode specific infrared excitation followed by broadband infrared multichannel probing to generate a transient spectrum. The recovery of the transient bleaching and absorption bands, following 2020 or 1953 cm−1 excitation, yields a v=1 CO-stretching lifetime T1=28±7 (1σ) ps. The transitions from v=1 vibrational states give rise to new absorption features in the transient spectra at 2008, 1994, 1941 and 1930 cm−1. The time evolution of these absorptions monitors rapid energy redistribution and equilibration (<10 ps) between the symmetric and asymmetric CO-stretching modes prior to ground state recovery.

Broadband femtosecond transient infrared spectroscopy using a 256 x 256 element indium antimonide focal-plane detector.

Application and characterization of large-format IR focal-plane arrays as detectors for ultrafast, high-resolution IR spectroscopy are discussed. We also present generation of broadband IR probe-reference pulses by use of collinear non-phase-matched geometry and shot-to-shot dual-track normalization to obtain transient spectra from broadly absorbing hydrogen-bonded systems. As much as 400-cm(-1)-wide coverage with 15-cm(-1) FWHM spectral resolution and +/-6.4 x 10(-4)(DOD = 3 x 10(-4)) baseline standard deviation (+/-1sigmas) is demonstrated near 2.9 microm.

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.

Femtosecond broadband infrared dual-beam spectroscopy of metal-carbonyl photochemistry

A novel spectroscopic method incorporating solid-state broadband infrared down and upconversion with 400 fs time resolution is described.