Excited Doublet Research Articles

Raman scattering investigation of the structural phase transition in single crystal KDy(WO4)2

The Raman scattering spectrum of a KDy(WO4)2 single crystal has been investigated in the frequency range 3–950 cm−1 at temperatures 2, 5, 25, 80, and 300 K. All 36 vibrational modes predicted by the group-theoretical analysis for the high-temperature phase were detected and their symmetries were determined. The analysis of the temperature behavior of the Raman spectra indicates that the monoclinic symmetry of the crystal remains unchanged upon the phase transition. Low-energy electronic transitions are observed between the levels of the ground multiplet 6H15/2 of the Dy3+ ion split by the crystal field of symmetry C2. It is established that in the region of the first excited Kramers doublet of the Dy3+ ion in the KDy(WO4)2 crystal, the Raman spectrum above the phase transition temperature of 6.38 K contains two lines (11.0 and 13.6 cm−1 at 25 K), while at lower temperatures it contains four lines (9.0, 16.2, 16.6, and 18.6 cm−1 at 2 K). This fact shows the presence of four nonequivalent dysprosium ions in the low-temperature phase. Three additional phonon lines (41.5, 76.7, 182.3 cm−1) observed in the low-temperature phase at 2 K also indicate that the primitive translation cell is doubled upon the phase transition. The measurements in an external magnetic field directed along the a-axis of the monoclinic cell revealed a considerable transformation of the scattering spectrum in the region of the first exited Kramers doublet of the Dy3+ ion in KDy(WO4)2. This transformation indicates a magnetic-field-induced phase transition.

Significant Enhancement of Energy Barriers in Dinuclear Dysprosium Single-Molecule Magnets Through Electron-Withdrawing Effects

The effect of electron-withdrawing ligands on the energy barriers of Single-Molecule Magnets (SMMs) is investigated. By introducing highly electron-withdrawing atoms on targeted ligands, the energy barrier was significantly enhanced. The structural and magnetic properties of five novel SMMs based on a dinuclear {Dy2} phenoxo-bridged motif are explored and compared with a previously studied {Dy2} SMM (1). All complexes share the formula [Dy2(valdien)2(L)2]·solvent, where H2valdien = N1,N3-bis(3-methoxysalicylidene) diethylenetriamine, the terminal ligand L = NO3(-) (1), CH3COO(-) (2), ClCH2COO(-) (3), Cl2CHCOO(-) (4), CH3COCHCOCH3(-) (5), CF3COCHCOCF3(-) (6), and solvent = 0.5 MeOH (4), 2 CH2Cl2 (5). Systematic increase of the barrier was observed for all complexes with the most drastic increase seen in 6 when the acac ligand of 5 was fluorinated resulting in a 7-fold enhancement of the anisotropic barrier. Ab initio calculations reveal more axial g tensors as well as higher energy first excited Kramers doublets in 4 and 6 leading to higher energy barriers for those complexes.

Valence one-electron and shake-up ionization bands of fluorene, carbazole and dibenzofuran

A comprehensive study of the He (I) ultra-violet photoelectron spectra of fluorene, carbazole and dibenzofuran is presented with the aid of one-particle Green’s Function calculations employing the outer-valence Green’s Function (OVGF) approach and the third-order algebraic diagrammatic construction [ADC(3)] scheme, along with Dunning’s correlation consistent basis sets of double and triple zeta quality (cc-pVDZ, cc-pVTZ). Extrapolations of the ADC(3) results for the outermost one-electron π-ionization energies to the cc-pVTZ basis set enable theoretical insights into He (I) measurements within ∼0.15eV accuracy, up to the σ-ionization onset. The lower ionization energy of carbazole is the combined result of mesomeric and electronic relaxation effects. OVGF/cc-pVDZ or OVGF/cc-pVTZ pole strengths smaller than 0.85 systematically corroborate a breakdown of the orbital picture of ionization at the ADC(3) level. Comparison is made with calculations of the lowest doublet–doublet excitation energies of the radical cation of fluorene, by means of time-dependent density functional theory (TDDFT).

Spin excitons in the unconventional superconducting and hidden order state of strongly correlated electrons

The formation of collective spin excitons below the single particle continuum is observed in numerous unconventional superconductors. CeCoIn5 is the most well established case for heavy fermion compounds. It is also the first example where the splitting of magnetic excitons by a magnetic field is observed for fields within the tetragonal plane. Contrary to expectations it is revealed as a doublet excitation. We explain the splitting as the result of a strongly anisotropic spin response described within the context of an Anderson lattice type model. Recently it was shown that collective spin excitations also appear within the hidden order phase of non- superconducting CeB6. It is a signature of the itinerant nature of spin response as opposed to the commonly used localized 4f approach in this compound. We show that the salient features of the spin exciton can be explained in an itinerant quasiparticle model supplemented by hidden and antiferromagnetic order.

Syntheses and Photophysical Investigations of Cr(III) Hexadentate Iminopyridine Complexes and Their Tris(Bidentate) Analogues

We report the preparation, photophysical characterization, and computed excited state energies for a family of Cr(III) complexes based on iminopyridine (impy) Schiff base ligands: compounds 1 and 2 feature hexadentate ligands where tren (tris-(2-aminoethyl)amine) caps three impy groups; compounds 3 and 4 are tris(bidentate) analogues of 1 and 2; compounds 2 and 4 contain methyl ester substituents to alter ligand donation properties relative to 1 and 3, respectively. Cyclic voltammograms exhibit multiple reversible ligand-based reductions; the hexadentate and tris(bidentate) analogues have almost identical reduction potentials, and the addition of ester substituents shifts reduction potentials by +200 mV. The absorption spectra of the hexadentate complexes show improved absorption of visible light compared to the tris(bidentate) analogues. Over periods of several hours to days, the complexes undergo ligand-substitution-based decomposition in 1 M HCl((aq)) and acetonitrile. For freshly prepared sample solutions in CH(3)CN, time-resolved emission and transient absorption measurements for 4 show a doublet excited state with 17-19 μs lifetime at room temperature, while no emission or transient absorption signals from the doublet states are observed for the hexadentate analogue 2 under the same conditions. The electronic structure contributions to the differences in observed photophysical properties are compared by extensive computational analyses (UB3LYP MD-DFT and TD-DFT-NTO). These studies indicate that the presence of nonligated bridgehead nitrogen atoms for 1 and 2 significantly reduce excited state doublet, quartet, and sextet energies and change the character of the low lying doublet states in comparison to species that show population of doublet excited states.

Ammonia in the hot core W 51-IRS2: 11 new maser lines and a maser component with a velocity drift

With the 100-m telescope at Effelsberg, 19 ammonia (NH3) maser lines have been detected toward the prominent massive star forming region W51-IRS2. Eleven of these inversion lines, the (J,K) = (6,2), (5,3), (7,4), (8,5), (7,6), (7,7), (9,7), (10,7), (9,9), (10,9), and (12,12) transitions, are classified as masers for the first time in outer space. All detected masers are related to highly excited inversion doublets. The (5,4) maser originates from an inversion doublet 340 K above the ground state, while the (12,12) transition, at 1450 K, is the most highly excited NH3 maser line so far known. Strong variability is seen not only in ortho- but also in para-NH3 transitions. Bright narrow emission features are observed, for the first time, in (mostly) ortho-ammonia transitions, at V ~ 45 km/s, well separated from the quasi-thermal emission near 60 km/s. These features were absent 25 years ago and show a velocity drift of about +0.2 km/s/yr. The component is likely related to the SiO maser source in W51-IRS2 and a possible scenario explaining the velocity drift is outlined. The 57 km/s component of the (9,6) maser line is found to be strongly linearly polarized. Maser emission in the (J,K) to (J+1,K) inversion doublets is strictly forbidden by selection rules for electric dipole transitions in the ground vibrational state. However, such pairs (and even triplets with (J+2,K)) are common toward W51-IRS2. Similarities in line widths and velocities indicate that such groups of maser lines arise from the same regions, which can be explained by pumping through vibrational excitation. The large number of NH3 maser lines in W51-IRS2 is most likely related to the exceptionally high kinetic temperature and NH3 column density of this young massive star forming region.

Ab initio study of vibronic transitions between x2π and 12Σ+ electronic states of HCP+ ion

The ground and low-lying excited doublet electronic states of the HCP+ ion were studied by means of multireference configuration interaction method. Vibronic energy levels of the X2? state of ?, ?, ?, and ? symmetry, up to the 2500 cm-1, have been calculated variationally, employing previously developed ab initio methods which take into account vibronic and spin-orbit interactions. Obtained vibronic wave functions were used to estimate transition moments between vibronic energy levels of the X2? and 12?+ electronic states. Results were compared to available experimental and theoretical data.

Induced quadrupole effects near a crossover in a tetragonal TbLiF4 sheelite in a strong magnetic field up to 50 T

The anomalies of magnetic properties of TbLiF4 caused by the interaction of the energy levels of a rare-earth ion in a strong magnetic field up to 50 T directed along the [100] and [110] axes are studied experimentally and theoretically. The jumps in magnetization M(H) and the maxima of the differential magnetic susceptibility dM(H)/dH are found in critical fields H c = 28 and 31 T, where the lower component of the excited doublet approaches the ground-state singlet of a Tb3+ ion. Based on the crystal-field model with known interaction parameters, we calculated the Zeeman effect and the magnetization and magnetic susceptibility curves for the TbLiF4 crystal, which adequately describe magnetic anomalies and critical parameters of a crossover. It is shown that the jumpwise change in the α- and γ-symmetry quadrupole interactions in TbLiF4 caused by changes in the corresponding quadrupole moments during the crossing of energy levels leads, in accordance with experiments, to a decrease in the critical field H c by approximately 4 T and an increase in the maximum of the differential susceptibility dM(H)/dH near the crossover more than twofold. This behavior can be considered as an analog of the induced quadrupole transition caused by a change of the ground state of the rare-earth ion during crossover.

Evolution of spin relaxation processes in LiY1−xHoxF4studied via ac-susceptibility and muon spin relaxation

We present measurements of magnetic field and frequency dependence of the low-temperature ($T$ = 1.8 K) ac-susceptibility and temperature and field dependence of the longitudinal field positive muon spin relaxation (\ensuremath{\mu}SR) for LiY${}_{1\ensuremath{-}x}$Ho${}_{x}$F${}_{4}$ with $x$ = 0.0017, 0.0085, 0.0408, and 0.0855. The fits of numerical simulations to the susceptibility data for the $x$ = 0.0017, 0.0085, and 0.0408 show that Ho-Ho cross-relaxation processes become more important at higher concentrations, signaling the crossover from single-ion to correlated behavior. We simulate the muon spin depolarization using the parameters extracted from the susceptibility, and the simulations agree well with our data for samples with $x$ = 0.0017 and 0.0085. The \ensuremath{\mu}SR data for samples with $x$ = 0.0408 and 0.0855 at low temperatures ($T$ 10 K) cannot be described within a single-ion picture of magnetic field fluctuations and give evidence for additional mechanisms of depolarization due to Ho${}^{3+}$ correlations. We also observe an unusual peak in the magnetic field dependence of the muon relaxation rate in the temperature interval 10--20 K that we ascribe to a modification of the Ho${}^{3+}$ fluctuation rate due to a field induced shift of the energy gap between the ground and the first excited doublet crystal field states relative to a peak in the phonon density of states centered near 63 cm${}^{\ensuremath{-}1}$.

X-ray Magnetic Circular Dichroism (XMCD) Study of a Methoxide-Bridged DyIII–CrIII Cluster Obtained by Fluoride Abstraction from cis-[CrIIIF2(phen)2]+

An isostructural series of dinuclear chromium(III)-lanthanide(III) clusters is formed by fluoride abstraction of cis-[CrF2(phen)2](+) by Ln(3+) resulting in LnF3 and methoxide-bridged Cr-Ln clusters (Ln = Nd (1), Tb (2), Dy (3)) of formula [Cr(III)(phen)2(μ-MeO)2Ln(NO3)4]·xMeOH (x = 2-2.73). In contrast to fluoride, methoxide bridges in a nonlinear fashion, which facilitates chelation. For 3, X-ray magnetic circular dichroism (XMCD) provides element-specific magnetization curves that are compared to cluster magnetization and susceptibility data acquired by SQUID magnetometry. The combination of XMCD and SQUID is able to resolve very small magnetic coupling values and reveals a weak Cr(III)-Dy(III) coupling of j = -0.04(3) cm(-1). The Dy(III) ion has a ground-state Kramers doublet of mJ = ±13/2, and the first excited doublet is found to be mJ = ±11/2 at an energy of δ = 57(21) cm(-1). The Cr(III) ion exhibits a uniaxial anisotropy of DCr = -1.7(1.0) cm(-1). Further, we observe that a weak anisotropic coupling of dipolar origin is sufficient to model the data, suggesting that methoxide bridges do not play a significant role in the magnetic coupling for the present systems.

Energy of partial A-body problem for 9ΛBe and 10ΛΛBe

The energy of the degenerate doublet (3+/2, 5+/2) of 9ΛBe, treating it as a partial nine-body system in the Λαα cluster model, has been calculated in the variational Monte Carlo framework. A simplified treatment, with the central two-body Urbana type ΛN and the three-body dispersive and two-pion exchange ΛNN forces along with the central two- and three-body correlations, is found to be adequate in explaining the energy of observed γ-ray transition from the excited degenerate doublet to the ground state. This partial nine-body model of 9ΛBe has been extended for the case of partial ten-body problem 10ΛΛBe in the ΛΛ + αα model where nucleonic degrees of freedom of as are taken into consideration ignoring antisymmetrization between two αs. The central two-body ΛN and ΛΛ and the three-body dispersive and two-pion exchange ΛNN forces, constrained by the Λp scattering data and the observed ground state energies of 5ΛHe and 6ΛΛ, are employed. The product type trial wavefunction predicts binding energy for the ground state considerably less than for the event reported by Danysz et al but however, consistent with the value deduced assuming a γ-ray of 3.04 MeV must have escaped undetected in the decay of the product 9ΛBe* → 9ΛBe + γ of the emulsion event 10ΛΛBe → π− + p + 9ΛBe* and for the excited 2+ state closer to the value measured in the Demachi-Yanagi event. The results of the present work are consistent with the earlier three- and four-body cluster model approaches where as are assumed to be structureless entities.

Electronic structure of a beryllium half‐sandwich complex, Be(η5‐C5H5)

AbstractAb initio electron propagator calculations on the electron affinities of the $ {\rm Be(\eta ^5-C_5H_5)}^{+} $ complex cation and electron detachment energies of the corresponding anion have been performed at the optimized geometry of the ground state of the neutral species. These results, obtained with a basis set that includes many diffuse and polarization functions, provide the relative energies of doublet states of $ {\rm Be(\eta ^5-C_5H_5)} $. In the former set of calculations, energy differences between the 2A1 ground‐state and various excited doublet states are associated with promotion of an unpaired electron from the 6a1 molecular orbital that consists chiefly of s functions on the Be nucleus to higher Be‐centered molecular orbitals that exhibit various patterns of interference between s, p, and d functions. Differences between electron detachment energies of the anion provide the energy separation between the radical's ground state and an excited state in which an electron is promoted from ligand‐centered π orbitals to 6a1. Dyson orbitals and pole strengths corresponding to correlated electron binding energies calculated with various diagonal self‐energy approximations confirm these qualitative pictures of the electronic structure of the lowest states of $ {\rm Be(\eta ^5-C_5H_5)} $. © 2012 Wiley Periodicals, Inc.

Magnetic Circular Dichroism Spectrum of the Molybdenum(V) Complex [Mo(O)Cl3dppe]: C-Term Signs and Intensities for Multideterminant Excited Doublet States

The molybdenum(V) complex [Mo(O)Cl(3)dppe] [dppe = 1,2-bis(diphenylphosphino)ethane] is considered as a model system for a combined study of the electronic structure using UV/vis absorption and magnetic circular dichroism (MCD) spectroscopy. In order to determine the signs and MCD C-term intensities of the chlorido → molybdenum charge-transfer transitions, it is necessary to take the splitting of the excited doublet states into sing-doublet and trip-doublet states into account. While transitions to the sing-doublet states are electric-dipole-allowed, those to the trip-doublet states are electric-dipole-forbidden. As spin-orbit coupling within the manifold of sing-doublet states vanishes, configuration interaction between the sing-doublet and trip-doublet states is required to generate the MCD C-term intensity. The most prominent feature in the MCD spectrum of [Mo(O)Cl(3)dppe] is a "double pseudo-A term", which consists of two corresponding pseudo-A terms centered at 27000 and 32500 cm(-1). These are assigned to the ligand-to-metal charge-transfer transitions from the p(π) orbitals of the equatorial chlorido ligands to the Mo d(yz) and d(xz) orbitals. On the basis of the theoretical expressions developed by Neese and Solomon (Inorg. Chem. 1999, 38, 1847-1865), a general treatment of the MCD C-term intensity of these transitions is presented that explicitly considers the multideterminant character of the excited states. The individual MCD signs are determined from the corresponding transition densities derived from the calculated molecular orbitals of the title complex (BP86/LANL2DZ).

Anisotropic magnetic properties and superzone gap formation in CeGe single crystal

Single crystals of CeGe and its non-magnetic analog LaGe have been grown by the Czochralski method. The CeGe compound crystallizes in the orthorhombic FeB-type crystal structure with the space group Pnma (#62). The anisotropic magnetic properties have been investigated for well oriented single crystals by measuring the magnetic susceptibility, electrical resistivity and heat capacity. It has been found that CeGe orders antiferromagnetically at 10.5 K. Both transport and magnetic studies have revealed large anisotropy, reflecting the orthorhombic crystal structure. The magnetization data at 1.8 K reveal metamagnetic transitions along the [010] direction at 4.8 and 6.4 T and along the [100] direction at a critical field of 10.7 T, while the magnetization along the [001] direction increases linearly without any anomaly up to a field of 16 T. From the magnetic susceptibility and the magnetization measurements it has been found that the [010] direction is the easy axis of magnetization. The electrical resistivity along the three crystallographic directions exhibits an upturn at TN, indicating superzone gap formation below TN in this compound. We have performed crystal electric field analysis on the magnetic susceptibility and the heat capacity data and found that the ground state is a doublet, and the energies of splitting from the ground state to the first and second excited doublet states were estimated to be 39 and 111 K, respectively.

Theoretical Studies of the Excited Doublet States of SF and SCl and Singlet States of SF2, SFCl, and SCl2

In previous work, we reported that the lowest-lying excited states of SF, SCl, SF(2), SFCl, and SCl(2) have recoupled pair bonds. In this study, we examine the analogous low-spin states--the (2)Σ(-) and (2)Δ states of SF and SCl and the excited singlet states of SF(2), SCl(2), and SFCl--which also possess recoupled pair bonds. In contrast to the excited states treated previously, the states studied in the present work have the same spin multiplicities as their respective ground states and are thus potentially observable via electronic excitation. Of particular interest are the minima on the (1)A″ potential energy surface of SFCl corresponding to bond-stretch isomers analogous to those found on the (3)A″ surface. In addition, we discovered that the first two excited states ((1)A″) accessible via vertical excitations from the ground state of SFCl have the electronic structure of the bond-stretch isomers. Thus, electronic excitation spectroscopic studies of SFCl could reveal a signature of the bond-stretch isomers. We will also present limited data on the lowest singlet Rydberg states of the triatomic species. Calculations were performed at the MRCI+Q/aug-cc-pV(Q+d,5+d)Z levels of theory.

Heavy atom nitroxyl radicals. VI. The electronic spectrum of jet-cooled H2PO, the prototypical phosphoryl free radical

The previously unknown electronic spectrum of the H(2)PO free radical has been identified in the 407-337 nm region using a combination of laser-induced fluorescence and single vibronic level emission spectroscopy. High level ab initio predictions of the properties of the ground and first two excited doublet states were used to identify the spectral region in which to search for the electronic transition and were used to aid in the analysis of the data. The band system is assigned as the B̃(2)A(')-X̃(2)A(') electronic transition which involves promotion of an electron from the π to the π∗ molecular orbital. The excited state r(0) molecular structure was determined by rotational analysis of high resolution LIF spectra to be r(PO) = 1.6710(2) Å, r(PH) = 1.4280(6) Å, θ(HPO) = 105.68(7)°, θ(HPH) = 93.3(2)°, and the out-of-plane angle = 66.8(2)°. The structural changes on electronic excitation, which include substantial increases in the PO bond length and out-of-plane angle, are as expected based on molecular orbital theory and our previous studies of the isoelectronic H(2)AsO, Cl(2)PS, and F(2)PS free radicals.

Signatures of spin-glass behavior in the induced magnetic moment system PrRuSi3

We have investigated the magnetic and transport properties of a ternary intermetallic compound PrRuSi3 using dc magnetization, ac susceptibility, specific heat, electrical resistivity, neutron diffraction, inelastic neutron scattering and muSR measurements. The magnetic susceptibility and specific heat data reveal the signatures of spin-glass behavior in PrRuSi3 with a freezing temperature of 9.8 K. At low magnetic fields, we observe two sharp anomalies (at 4.9 and 8.6 K) in magnetic susceptibility data. In contrast, the specific heat data show only a broad Schottky-type anomaly centered around 10 K. However, muSR reveals very low frequency coherent oscillations at 1.8 K with an onset of fast relaxation below 12 K indicating a long range magnetically ordered ground state with very small moment. On the other hand, no magnetic Bragg peaks are observed in low temperature neutron diffraction data at 1.8 K. These two contradictory ground states, spin-glass versus magnetic order, can be explained if the spin-glass behavior in PrRuSi3 is considered due to the dynamic fluctuations of the crystal field levels as has been proposed for spin-glass behavior in PrAu2Si2. Two sharp inelastic excitations near 2.4 meV and 14.7 meV are observed in the inelastic neutron scattering (INS) spectra between 4 K and 50 K. Further, exchange coupling J_ex obtained from the analysis of INS data with CEF model provides evidence for the spontaneously induced magnetic order with a CEF-split singlet (Gamma_t4) ground state. However, the exchange coupling seems to be close to the critical value for the induced moment magnetism, therefore we tend to believe that the dynamic fluctuations between the ground state singlet and excited doublet CEF levels is responsible for spin-glass behavior in PrRuSi3.

Increase of probe beam light-induced polarization rotation via accumulation of coherent oscillations

We study possibilities of the method of accumulation of the coherent-nonstationary response of the medium for amplifying the polarization rotation of probe radiation in conditions of a cascade two-photon resonance. The probe field couples the ground level nS1/2 of an alkali metal atom with the excited doublet nP1/2,3/2, while the monochromatic pump field couples this doublet with a higher excited state n’S1/2. We obtain analytic expression for the rotated component of the probe field polarization. It is shown that consistent switching by π the phase of the input probe field may create in the tail portion of its rotated component a separate light pulse with more than an order of magnitude higher intensity, which is a desired result for polarization laser spectroscopy.

Ultrafast Intersystem Crossing and Spin Dynamics of Zincmeso-Tetraphenylporphyrin Covalently Bound to Stable Radicals

tert-Butylphenylnitroxide (BPNO(•)) and α,γ-bisdiphenylene-β-phenylallyl (BDPA(•)) stable radicals are each attached to zinc meso-tetraphenylporphyrin (ZnTPP) at a fixed distance using one of the ZnTPP phenyl groups. BPNO(•) and BDPA(•) are oriented para (1 and 3, respectively) or meta (2 and 4, respectively) relative to the porphyrin macrocycle. Following photoexcitation of 1-4, transient optical absorption spectroscopy is used to observe excited state quenching of (1)*ZnTPP by the radicals and time-resolved electron paramagnetic resonance (TREPR) spectroscopy is used to monitor the spin dynamics of the paramagnetic product states. The presence of BPNO(•) or BDPA(•) accelerates the intersystem crossing rate of (1)*ZnTPP about 10- to 500-fold in 1-4 depending on the structure compared to that of (1)*ZnTPP itself. In addition, the lifetime of (3)*ZnTPP in 1 is shorter than that of (3)*ZnTPP itself as a result of enhanced intersystem crossing (EISC) from (3)*ZnTPP to the ground state. The TREPR spectra of the three unpaired spins produced within 1 and 2 show spin-polarized excited doublet (D(1)) and quartet (Q) states and subsequent formation of a spin-polarized ground state radical (D(0)). All three signals are absorptive for 1 and emissive for 2. Polarization inversion of the Q state is observed on a tens of nanoseconds time scale in 2, while no polarization inversion is observed for 1. The lack of polarization inversion in 1 is attributed to the short lifetime of the doublet-quartet manifold as a result of the very large exchange interaction. The TREPR spectra of 3 and 4 show ground state radical polarization at X-band (9.5 GHz) at room temperature, but not at 85 K, and similarly no polarization is observed at W-band (94 GHz). No evidence of excited doublet or quartet states is observed, indicating that the exchange interaction is both weak and temperature dependent. These results show that although ultrafast EISC produces (3)*ZnTPP within 1-4, the magnitude of the exchange interactions between the three relevant spins in the resulting (3)*ZnTPP-BPNO(•) and (3)*ZnTPP-BDPA(•) systems dramatically alters their spin dynamics.

Ab Initio Analysis and Harmonic Force Fields of Gallium Nitride Nanoclusters

Gallium nitride (GaN) clusters are analyzed to set approaches for more extended calculations at the nanoscale. We test the atom components and very small clusters using the most sophisticated compound methods such as G1−G3, CBS, W1, and a flavor of DFT (B3PW91) using several sizes and qualities of basis sets. Results are compared with very precise experimental information when available. Interestingly, the B3PW91 yields results comparable to the high-quality compound methods. For negative ions, it is difficult to assess the quality of the methods; the electron affinity (EA) calculations, as expected, yield better results when diffuse functions are used. All ionization potentials (IPs) are well reproduced by all methods, but the best results are obtained with B3PW91 for the Ga atom and with the compound methods for N. Among the compound methods, the W1 ones use the largest basis sets with 93 functions (which include two sets of g-functions) for one gallium atom. Geometry optimizations are performed with MP2 for the G-methods, HF for the CBS-methods (except QB3), and B3LYP for the CBS-QB3 and all W1 methods. G3 followed by B3PW91 yields the best result for the Ga quartet excited state, and there is little difference for the excited doublet of N, among the compound methods. In general all calculated IPs and EAs are in good agreement with existing experimental data. We also performed extended calculations of bigger GaN clusters such as GaxNy where 6 < x ≈ y < 19 using B3PW91/6-311G(d). Finally, we calculate second derivative and thus the vibrational spectra for all clusters studied. We generate harmonic force fields using the procedure Fuerza and averaged the force field parameters and use them in a simple heating molecular dynamics calculation that yields an acceptable value for the heat capacity.