Onset of carbon–carbon bonding in the Nb<sub>5</sub>C<sub>y</sub>(y = 0–6) clusters: a threshold photo-ionisation and density functional theory study

Gas-phase bimetallic tantalum-zirconium-carbide clusters are generated using a constructed double ablation cluster source. The Ta 3 ZrC y ͑y =0-4͒ clusters are examined by photoionization efficiency spectroscopy to extract experimental ionization energies ͑IEs͒. The IE trend for the Ta 3 ZrC y cluster series is reasonably similar to that of the Ta 4 C y cluster series ͓V. Dryza et al., J. Phys. Chem. A 109, 11180 ͑2005͔͒, although the IE reductions upon carbon addition are greater for the former. Complementary density functional theory calculations are performed for the various isomers constructed by attaching carbon atoms to the different faces of the tetrahedral Ta 3 Zr cluster. The good agreement between the experimental IE trend and that calculated for these isomers support a 2 ϫ 2 ϫ 2 face centered cubic nanocrystal structure for Ta 4 ZrC 4 and nanocrystal fragment structures for the smaller clusters.

Section: B Pie Experimentsmentioning

confidence: 99%

Section: Dft Calculated Isomersmentioning

confidence: 99%

Threshold photoionization and density functional theory studies of bimetallic-carbide nanocrystals and fragments: Ta3ZrCy (y=–4)

Dryza

Metha

2009

“…Previous experience in our group, using the B3P86 functional, confirms the tendency of this functional to predict IPs that are 0.3-1.0 eV higher than experimentally measured values. [23][24][25] Using the smallest basis set combination at the MRCI and MRCI+ Q levels, the predicted IPs of 4.55 and 4.80 eV, respectively, are substantially below the experimental value. The addition of unlinked quadruple excitations increased the calculated IP value by 0.25 eV; however the resultant value is still Ϸ0.6 eV below the experimental value.…”

Section: Ip Calculationsmentioning

confidence: 99%

Excited states of Nb3N2 and Nb3C2: Density functional theory, CASSCF, and MRCI studies

Addicoat

Metha

2009

Self Cite

Complete active space self-consistent field ͑CASSCF͒ and multireference configuration interaction ͑MRCI͒ methods are used to investigate the Nb 3 N 2 and Nb 3 C 2 clusters in order to determine the agreement between multireference methods, density functional theory ͑DFT͒, and experiment. These two clusters are ideal candidates to study as the known spectroscopy can serve to validate the computational results, yet there is still room for the calculations to inform further spectroscopic experiments. We find that the MRCI leading configuration for each of the ground states is in agreement with that predicted by DFT but only accounts for up to 70% of the total configuration. CASSCF and DFT geometries are also in general agreement. Transition energies between the neutral and cationic manifolds are found to be poorly predicted by MRCI relative to the computationally cheap DFT method. For Nb 3 C 2 we find that a higher energy isomer may have an electronic transition in the spectral vicinity as the lowest energy isomer.

“…Upon supersonic expansion, the internal vibronic temperature of all clusters formed in the ablation process is ϳ300 K, as reported in our previous papers. 42,43 The neutral clusters formed in the laser ablation process are ionized with the frequency doubled output of a Nd:YAG pumped dye laser ͑220-280 nm͒ and extracted perpendicularly using deflection plates and an Einzel lens into the TOF-MS flight region and onto a double microchannel plate detector. The resulting cluster signal is then amplified ϫ25 with a commercial preamplifier ͑Stanford SR445͒ and delivered to a digital oscilloscope ͑LeCroy 9350 a.m., 500 MHz͒ for averaging ͑1000 laser shots͒ before being sent to a PC for analysis.…”

Section: A Experimental Methodsmentioning

confidence: 99%

“…[42][43][44] This is attributed to the nature of the B3P86 functional. Therefore, the IEs are corrected with respect to the RhHo 2 bare metal cluster as we are primarily concerned with how the IE changes with respect to the sequential addition of oxygen atoms.…”

Section: Comparison Between Experimental and Theoretical Datamentioning

confidence: 99%

Photoionization efficiency spectroscopy and density functional theory investigations of RhHo2On (n=–2) clusters

Gentleman

Addicoat

Dryza

et al. 2009

Self Cite

The experimental and theoretical adiabatic ionization energies ͑IEs͒ of the rhodium-holmium bimetallic clusters RhHo 2 O n ͑n =0-2͒ have been determined using photoionization efficiency spectroscopy and density functional theory ͑DFT͒ calculations. Both sets of data show the IE of RhHo 2 O to be significantly lower than the values for RhHo 2 and RhHo 2 O 2 , which are found to be similar. This indicates that there are significant changes in electronic properties upon sequential addition of oxygen atoms to RhHo 2 . The DFT investigations show that the lowest energy neutral structures are a C 2v triangle for RhHo 2 , a C 2v planar structure for RhHo 2 O where the O atom is doubly bridged to the Ho-Ho bond, and a C 2v nonplanar structure for RhHo 2 O 2 , where the O 2 is dissociative and each O atom is doubly bridged to the Ho-Ho bond in the cluster above and below the RhHo 2 trimer plane. Good correlation between the experimental and computational IE data imply that the lowest energy neutral structures calculated are the most likely isomers ionized in the molecular beam. In particular, the theoretical adiabatic IE for the dissociative RhHo 2 O 2 structure is found to compare better with the experimentally determined value than the corresponding lowest energy O 2 associative structure.