Ultrafast infrared study of the ultraviolet photodissociation of Mn2(CO)10

Abstract

The 310 nm photodissociation of dimanganese decarbonyl, Mn2(CO)10, in cyclohexane has been studied using ultrafast infrared spectroscopy. Subpicosecond IR detection near 5 μm, in the region of carbonyl stretch vibrations, is carried out using a frequency-resolved broad (>100 cm−1) IR probe pulse. The evolution of infrared spectra provide information on Mn2(CO)10 and its photoproducts. In the terminal carbonyl region (1970–2050 cm−1), bleach signals are observed due to loss of the parent compound. A broad, featureless absorption appears promptly and narrows upon vibrational cooling (on the 50 ps time scale) to reveal IR spectral features consistent with those previously assigned to two photoproducts, Mn(CO)5 and Mn2(CO)9. The bleach signals partially recover, indicating ground state recovery of vibrationally excited Mn2(CO)10, which is consistent with previous reports of geminate recombination. Mn2(CO)9 signal appearance times are 54(4) ps for the terminal CO band at 2052 cm−1 and 31(5) ps for the bridge band at 1760 cm−1. The direct observation of the bridging band establishes 31 ps as an upper limit for the bridge bond formation. The time dependence of the signal is probably due primarily to vibrational cooling of low frequency modes. The times are somewhat longer than the shorter of two times measured in the visible region and attributed to low frequency mode thermalization by Zhang and Harris [J. Chem. Phys. 95, 4024 (1991)]. Vibrational coherence effects were observed at early times (close to the vibrational dephasing time).

Ultrafast studies of gold, nickel, and palladium nanorods

“…PFID is a commonly observed for negative delay times of an IR probe pulse that experiences absorption ͑either by the sample or, as in the present case, in the path prior to reaching the sample͒ in ultrafast infrared spectroscopy. [78][79][80] For the higher frequency probes, 1800-2600 cm −1 , a similar behavior is observed with a transient absorption ͑ϳ8 mOD͒ that partially decays ͑by at least 50%͒ to a long-lived signal. The fit decay time is ϳ0.6 ps in each case.…”

Modified relaxation dynamics and coherent energy exchange in coupled vibration-cavity polaritons

“…Figure 6a shows examples of the oscillatory signals we observe. The oscillations start at negative time delays when the probe pulse arrives at the sample before the excitation pulse, suggesting that the probe pulse generates a coherence that the excitation pulse interacts with, as observed in perturbed free-induction decays45565758. However, the periods of the oscillations we observe are insensitive to probe frequency or pump pulse intensity, which is in stark contrast to the highly probe-frequency dependent perturbed free-induction decays or uncoupled Rabi oscillations (‘flopping')59.…”

Organometallic photochemistry at the end of its first century

“…Various studies established that this species reacted with 2-methyltetrahydrofuran, 2-MTHF, to form Mn 2 (CO) 9 (2-MTHF) and with PPh 3 doped matrices to form Mn 2 (CO) 9 (PPh 3 ) [89]. While the Mn(CO) 5 radicals were not observed in these matrix studies (a common feature in frozen matrices due to the rapid recombination of radicals within the solvent cages), they have since been directly observed by time-resolved IR studies [90]. A strong wavelength dependence has been found for the photochemistry of Mn 2 (CO) 10 with Mn-Mn bond breaking dominating at lower energies, while CO-loss is more important at higher energies, Scheme 10.…”