Abstract
High-resolution vacuum ultraviolet photoabsorption measurements in the wavelength range of 115–320 nm (10.8–3.9 eV) have been performed together with comprehensive relativistic time-dependent density functional calculations (TDDFT) on the low-lying excited sates of tungsten hexacarbonyl, W(CO)6. The higher resolution obtained reveals previously unresolved spectral features of W(CO)6. The spectrum shows two higher-energy bands (in the energy ranges of 7.22–8.12 eV and 8.15–9.05 eV), one of them with clear vibrational structure, and a few lower-energy shoulders in addition to a couple of lower-energy metal-to-ligand charge-transfer (MLCT) bands reported in the literature before. Absolute photoabsorption cross sections are reported and, where possible, compared to previously published results. On the basis of this combined experimental/theoretical study the absorption spectrum of the complex has been totally re-assigned between 3.9 and 10.8 eV under the light of spin–orbit coupling (SOC) effects. The present comprehensive knowledge of the nature of the electronically excited states may be of relevance to estimate neutral dissociation cross sections of W(CO)6, a precursor molecule in focused electron beam induced deposition (FEBID) processes, from electron scattering measurements.
Highlights
The electronic structure of tungsten hexacarbonyl, W(CO)6, has previously been studied by using a variety of different experimental and theoretical methods, with experiments including vacuum ultraviolet experiments in the wavelength range of 125–350 nm [1,2,3,4,5], and electron energy loss [6,7,8], photoelectron [9,10], photoionisation [11] and electron momentum [12,13] spectroscopy
Electron-induced reactions in focused electron beam induced deposition (FEBID) processes are initiated by low-energy secondary electrons rather than the high-energy primary beam impinging on the surface where dissociative electron attachment (DEA) processes are relevant, at those energies electron impact excitations yielding neutral dissociation are prevalent in detriment to DEA [25]
The time-dependent density functional theory (TDDFT) absorption spectrum of W(CO)6 without spin–orbit coupling (SOC) is depicted in Figure S2 of Supporting Information File 1
Summary
The electronic structure of tungsten hexacarbonyl, W(CO), has previously been studied by using a variety of different experimental and theoretical methods, with experiments including vacuum ultraviolet experiments in the wavelength range of 125–350 nm [1,2,3,4,5], and electron energy loss [6,7,8], photoelectron [9,10], photoionisation [11] and electron momentum [12,13] spectroscopy. From the experimental point of view, such electron impact excitation spectra cannot be recorded with higher energy resolution than with optical spectra [31], making the latter an important tool to uncover features that may be not attained even in pseudo-optical conditions (high electron impact energy and low scattering angle) [32] Another relevant aspect highlighted by Qi et al [5] in the 30–160 nm wavelength region pertains to the similarity observed in the qualitative behaviour of neutral photodissociation and UV photoabsorption below the first ionisation energy, where CO ligand ejection occurs. As part of an ongoing effort to fully characterize the electron-induced fragmentation channels of W(CO), as needed for FEBID simulations, the purpose of the present work is to provide a high-resolution vacuum ultraviolet (VUV) absorption spectrum, representative of transitionmetal carbonyl complexes for which unresolved spectral features remain to be solved, with a description as complete as possible of the electronic states
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