Femtosecond Infrared Studies of the Dissociation and Dynamics of Transition Metal Carbonyls in Solution

Abstract

The ultrafast dynamics of the dissociation of M(CO) 6 (M ) Cr, W, Mo) in alkane solutions were studied by femtosecond IR spectroscopy. After UV photolysis at 295 nm, both the bleach of the parent molecules and the absorption of the pentacarbonyl intermediate were probed with 240 fs time resolution. Oscillatory perturbed free induction decay signals before t ) 0 were observed and well characterized by realistic parameters of the system. The bleach recovery dynamics were found to be wavelength dependent, indicating that hot parent molecules are formed and that the bleach recovery time is determined by the vibrational cooling time. The measured percentage bleach recovery in n-heptane is less than the expected value calculated from the photosubstitution quantum yield measurements, suggesting that the initial recovery of the bleach is faster than our time resolution. The kinetics in the A 1 vibrational mode region of the pentacarbonyl species have been measured to probe the formation and decay of the nascent product. The absorption of the product rises with an instrument response limited rate indicating that the formation of the product is much faster than 240 fs. The long time kinetics in this region reflect the vibrational cooling of the product. A fast decay with time constant of less than 300 fs is present in all the wavelengths probed, and its spectrum appears to resemble the early time spectrum of the hot pentacarbonyl species. This fast decay, observed in all three different metal carbonyls, is attributed to the fast geminate recombination of the pentacarbonyl with photodissociated CO ligand after only one to two collisions with the solvent cage.

Time resolved infrared studies of C-H bond activation by organometallics

“…A schematic representation of the laser system is shown in 2.1 on page 8, and it has been described previously [2,3]. A summary of the laser is also provided in appendix B on page 135, which contains important parameters.…”

Watching Photoinduced Chemistry and Molecular Energy Flow in Solution in Real Time

“…What may be straightforward for isolated molecules [4,5] is more difficult in solution owing to complex interactions with the molecular environment and broad spectra often preventing unambiguous assignments. [6] Nevertheless, bond fission, [7][8][9][10][11][12][13] structural isomerization, [14,15] intramolecular rearrangements, [16,17] solvation, [18,19] inter-and intramolecular energy transfer, [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] internal conversion, [19,39] as well as electron [39][40][41] and proton transfer [42][43][44] are only few of the numerous elementary processes in the condensed phase that have been studied recently by time-resolved femtosecond (fs) spectroscopy. Good overviews that highlight important work and pioneering experiments are given in references [5,6,…”

Investigation of organometallic reaction mechanisms with one and two dimensional vibrational spectroscopy

“…Rubitsov and coworkers recently reported this effect in a small organic molecule and stressed its potential importance for enhancing cross peak intensities at long T w [236]. We do not observe this effect in [253,256]. The fast relaxation of the low frequency modes in comparison to the high frequency CO stretches prevents vibrational energy from building up in them; thus, the modes do not have sufficient population to strongly contribute to the 2D-IR spectra.…”