Ultraviolet photodissociation of gas-phase iron pentacarbonyl probed with ultrafast infrared spectroscopy

Abstract: It is well known that ultraviolet photoexcitation of iron pentacarbonyl results in rapid loss of carbonyl ligands leading to the formation of coordinatively unsaturated iron carbonyl compounds. We employ ultrafast mid-infrared transient absorption spectroscopy to probe the photodissociation dynamics of gas-phase iron pentacarbonyl following ultraviolet excitation at 265 nm and 199 nm. After photoexcitation at 265 nm, our results show evidence for sequential dissociation of iron pentacarbonyl to form iron tricarbonyl via a short-lived iron tetracarbonyl intermediate. Photodissociation at 199 nm results in the prompt production of Fe(CO)₃ within 0.25 ps via several energetically accessible pathways. An additional 15 ps time constant extracted from the data is tentatively assigned to intersystem crossing to the triplet manifold of iron tricarbonyl or iron dicarbonyl.

Experimental Data: All data are saved as a .csv file. Each transient .csv file is labeled according to molecule, pump wavelength, pressure, file contents, polarization, pump laser power, and a date (e.g. IP199_1.5torr_trans_magic_330uW_08Jun2020.csv). The first column contains frequencies (in cm^-1) while the first row indexes each time delay (in ps). Transient spectra at select time delays, i.e. the transient data presented in Figures 1, 3, and Section S3.2, are from the corresponding "_PFIDfiltered_" datasets.

Computational Data: Files xxx_harm.out (xxx = feco5, feco4, feco3, feco2, feco, and co) are output files from harmonic frequency calculations performed at the geometries reported above. Files fe_co5_co4_x.out (x = 0, 2, 4, 6, 8, and 10) correspond to EOM-EE-CCSD(dT) calculations along the IP to 4 pathway seen in Fig. 5 (left). Files fe_co5_co3_x.out (x = 0, 2, 4, 6, 8, and 10) correspond to EOM-EE-CCSD(dT) calculations along the IP to 3 pathway seen in Fig. 5 (right). File fe_co4_tet.out corresponds to the EOM-EE-CCSD(dT) calculation at the tetrahedral 4 geometry seen in Fig. 6 (left). Files fe_co4_co3_x.out (x = 0, 2, 4, 6, 8, and 10) correspond to EOM-EE-CCSD(dT) calculations along the 4 to 3 pathway seen in Fig. 6 (right). An additional README file summarizes the outputs.