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Dimethyl zinc Zn(CH3)2 in He was photolyzed at 223 nm in a flow cell at 298 K, and the photoproduct ZnCH3 was detected with laser-induced fluorescence via the A˜2E − X˜2A1 transition. The excitation spectrum showed the sharp peaks of the K structure of the 601(v′= 0 ← v6 = 1) vibrational band in the A˜2E1/2 − X˜2A1 and A˜2E3/2 − X˜2A1 transitions. A spectroscopic simulation well-reproduced not only the transition energies of the K subbands but also the intensity alternation of the peaks due to the nuclear spin statistics of the three hydrogen atoms of the methyl group. The vibrational frequency of the ν6 mode of the X˜2A1 state has been determined to be 587 cm−1, which replaces the previously reported value of 315 cm−1. The transition energies of the band origins are 23 362 and 23 617 cm−1 for the 601 bands whose upper states are A˜2E1/2 and A˜2E3/2, respectively. Based on the relevant literature studies, we have shown that the 0–1 band of the degenerate vibration of a symmetric top is allowed in the transition between electronic states at least one of which is degenerate.

Methyl zinc CH3Zn generated in the photolysis of dimethyl zinc (CH3)2Zn at 223 nm was detected with laserinduced fluorescence (LIF) via the à 2E − X̃ 2A1 transition. The time-resolved LIF intensity of the level X̃ 2A1, 00 grew with time, indicating that the nascent CH3Zn was highly vibrationally excited. The He-pressure dependence of the growth rates of the LIF intensity was analyzed by the kinetic scheme with a rate-determining step, giving the rate coefficient for vibrational relaxation to the X̃ 2A1, 00 level to be [8.2 ± 0.9(2σ)] × 10− 13 cm3 molecule− 1 s− 1. The probability of vibrational relaxation of CH3Zn per collision with He nicely correlates with those of nonor less-polar diatomic molecules.

We investigated the photodissociation dynamics of CpCo(CO)2 (cyclopentadienylcobalt dicarbonyl) in metal-to-ligand charge transfer (MLCT) bands. By employing DFT calculations, the absorption band (210–240 nm) was characterized as a charge transfer from the Co center to the Cp (cyclopentadienyl, C5H5) ligand. Ion imaging was utilized to analyze the CO fragments and coordinatively unsaturated complexes (CpCoCO, CpCo, and CoC3H3) across the entire MLCT band. Measuring the production yields of individual unsaturated complexes as a function of photolysis wavelength by considering wavelength dependence indicated the involvement of several photochemical pathways: the first photodissociation and sequential dissociation of CpCo(CO)2, and the second photodissociation of unsaturated intermediates within the pulse duration of the photolysis laser. The recoil velocity shifts of CpCo and CoC3H3 were attributed to the onset of the sequential dissociation of CpCoCO. Evidence for the second photodissociation of CpCoCO was obtained through the matching of linear momenta between the CO(v = 0, 1) and CpCo fragments. The DFT calculations performed to determine the electronic structures and potential energy curves for photoinduced CO loss in CpCo(CO)2 and CpCoCO supported our interpretation of the experimental results. This study presents a practical approach to selectively detecting specific processes among the mixture of products and intermediates when photolyzing transition-metal carbonyls, as their concurrent generation is unavoidable in laser-based experiments.

Ultraviolet photochemistry of iron pentacarbonyl, Fe(CO)(5), was investigated with resonantly enhanced multiphoton ionization (REMPI) spectroscopy and ion imaging. The REMPI spectrum of CO photofragments, generated by ultraviolet irradiation of Fe(CO)s, showed the generation in the highly vibrationally excited states with v = 11-15. Analysis of the band intensities observed in the 213-235 nm region indicated that the high-v CO generation was maximized at around 220 nm. Generation yields of the coordinatively unsaturated intermediates, Fe(CO)(n=1-4), were measured as a function of the photolysis wavelength using a nonresonant detection scheme. The yield spectrum of FeCO was correlated with that of the high-v CO fragments, suggesting high-v CO generation in the photo- dissociation of FeCO. The density functional theory calculations of the excited states of FeCO showed an intense photoabsorption to the metal-centered state near 220 nm. The theoretical results were consistent with the interpretation of FeCO + by -> Fe + high-v CO, which was experimentally indicated. The momentum distribution obtained from the velocity distributions of Fe, Fe(CO)(4), and CO fragments further supported that Fe is the counter-product of the high-v CO fragment. The present results provided selective observation of the photochemistry of the unsaturated iron carbonyl complexes, which has not been well elucidated in laser-based experiments because of the uncontrollable sequential photodissociation producing mixed Fe(CO)(n) intermediates.

The highly rotationally excited states in the A(2)Sigma(+)-X-2 Pi(Omega), band of NO were investigated by laser-induced fluorescence and multi-photon ionization spectroscopy. The rotational states with J up to 80.5 were prepared by CH3ONO photodissociation in the S-1 and S-2 excited states for spectroscopic measurements. In total, 3890 lines of nine vibronic bands were analyzed. The observed line positions deviated from the values calculated using the previous molecular constants as J increased in the J > 50.5 region. The sextet-order centrifugal distortion constants were determined for the A(2)Sigma(+) and X-2 Pi(Omega), states so that the transition frequencies associated with the high -J states could reproduce the observed results within the experimental accuracy. The band origin values, whose errors have been discussed in previous studies, were refined in the present analysis. The experimental condition to suppress the rotational relaxation of the high-J states was examined, enabling us to determine the higher-order centrifugal distortion constants. (C) 2021 Elsevier Inc. All rights reserved.

The photodissociation dynamics of the heteroleptic Co(CO)3NO complex were investigated in the metal-to-carbonyl (CO) ligand charge-transfer band to compare the reactivity of the CO and nitrosyl (NO) ligands. The final state distributions of both the CO and NO fragments were measured using resonance-enhanced multiphoton ionization (REMPI) spectroscopy and velocity-map ion-imaging. The primary CO photofragment was differentiated from the secondary fragments of the subsequent unimolecular decomposition of coordinatively unsaturated intermediates by comparing the momentum distributions. The internal energy of the Co(CO)2NO intermediate was sufficiently high (≥348 kJ/mol) to be generated in the electronic excited state, indicating the occurrence of the primary CO elimination on an excited state. The NO fragments exhibited two velocity components. The analysis of the final state distributions suggested that the higher- and lower-kinetic-energy components originated from the direct primary elimination and sequential elimination, respectively. The direct photoelimination through a transiently bent ligand conformation was illustrated on the basis of a two-dimensional REMPI approach and time-dependent density functional theory calculations. The present results of both ligands demonstrate the correlation between elimination mechanisms and possible ligand conformations in the electronic excited state.