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1.
Medium‐sized phosphorus cluster cations were generated by laser ablation of red phosphorus and investigated by the method of collision‐induced dissociation mass spectrometry. Experimental results show that the primary dissociation channels of phosphorus cluster cations of P + 2m+1 (6 ≤ m ≤ 11) are all characterized by the loss of P 4 unit. For larger cluster cations, their dissociation pathways were more complex. For those magic cations of P + 8k+1 observed previously, their dissociation pathways progressively change from the loss of P 4 unit (for k = 3) to the loss of P 8 unit (for k = 4, 5). A new dissociation pathway characterized by the loss of P 10 unit was also indentified for larger cations of P + 8k+1 (6 ≤ k ≤ 8). Theoretical calculation also shows that, for cations of P + 2m+1 (4 ≤ m ≤ 10), the dissociation channel characterized by the loss of P 4 unit is more energetically favorable than other dissociation channels, which is in good agreement with the experimental results. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
2.
Photofragment spectroscopy of N 2 + has been studied in the wavelength range 343–404 nm using an excimer-pumped dye laser with a spectral resolution of 0.2 cm ?1. The observed bands are assigned to transitions from the v″=23?26 levels of the X 2Σ g + state to highlying rovibrational levels ( v′≈46–48) of the B 2Σ u + state, forming quasibound (predissociating) states above the dissociation limit N +( 3 P)+N( 4 S 0). Measurement of the photofragment kinetic energies allows to establish an absolute energy scale for the transitions with respect to the dissociation limit. Molecular constants for the lower and upper states of the observed transitions are determined. The measurements allow the first direct determination of the N 2 + dissociation energy D 0 0 (N 2 + ). Some high-resolution (0.04 cm ?1) measurements show the fine-structure splitting and lifetime broadening of the excitation lines. 相似文献
3.
Ab initio valence bond calculations for the ground and excited states of HF and HF + are presented. Total energies, equilibrium geometries, dissociation energies, dipole moments, and spectroscopic constants for HF and HF + have been calculated. The photoelectron spectrum of HF has been examined and interpreted by means of the valence bond formalism. The ground state of the protonated species H 2F + has been investigated. 相似文献
4.
Summary This paper presents a detailed ab initio study of the molecules P 2O and P 2O + at the Hartree-Fock, and Multi-Reference Single and Double Excitation Configuration Interaction levels. An analysis of the geometries and relative stabilities of both molecules is presented, together with a discussion of the dissociation channels and of the electronic spectrum of linear P 2O. The results for the ionic species P 2O + suggest a cyclic geometry for this molecule, as indicated by the calculated vibrational frequencies. The calculations also indicate a surface crossing at a relatively low energy which might lead to P 2O dissociation and may hence be one of the factors contributing to the failure to detect it at room temperatures. 相似文献
5.
The potential energy surface of CO 22+ ( 3Σ g?) is investigated with HF, MP2, MP4, CBS‐Q, G1, G2MP2, G2, G3B3, and B3LYP/6‐311++G(3df,3pd) methods. Density functional theory shows the lowest dissociation channel of this compound to be the formation of CO + ( 2Σ +)+O + ( 4S u) and to have a barrier of around 2 eV as well as a dissociation energy of around ?3.2 eV. Thus we propose that with enough correlation it is possible to accurately predict the energies of dissociation and barrier widths and heights to test for the stability of a particular molecular species. We also propose a refinement of current understanding by observing HOMO–LUMO gaps, Lowdin and Mulliken bond orders (to test for bond orbital overlap and hence qualitatively describe bonding and fragmentation in these complexes) and predicted spectrum for such studies as ZEKE spectroscopy (to study cationic states) and REMPI (to study the first excited states) of these class of molecules and, we hope, provide future insight into larger and more interesting systems. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 相似文献
6.
Several polyatomic ions in inductively coupled plasma–mass spectrometry are studied experimentally and by computational methods. Novel calculations based on spin-restricted open shell second order perturbation theory (ZAPT2) and coupled cluster (CCSD(T)) theory are performed to determine the energies, structures and partition functions of the ions. These values are combined with experimental data to evaluate a dissociation constant and gas kinetic temperature ( Tgas) value. In our opinion, the resulting Tgas value can sometimes be interpreted to deduce the location where the polyatomic ion of interest is generated. The dissociation of N 2H + to N 2+ leads to a calculated Tgas of 4550 to 4900 K, depending on the computational data used. The COH + to CO + system yields a similar temperature, which is not surprising considering the similar energies and structures of COH + and N 2H +. The dissociation of H 2CO + to HCO + leads to a much lower Tgas (< 1000 to 2000 K). Finally, the dissociation of H 2COH + to HCOH + generates a Tgas value between those from the other H xCO + ions studied here. All of these measured Tgas values correspond to formation of extra polyatomic ion in the interface or extraction region. The computations reveal the existence of isomers such as HCO + and COH +, and H 2CO + and HCOH +, which have virtually the same m/ z values and need to be considered in the interpretation of results. 相似文献
7.
State-of-the-art ab initio studies demonstrate that the reaction Pd + + CH 3I → PdCH 2I + + H . is endothermic by ca. 20 kcal/mol, which translates into a bond dissociation energy ( BDE) of ca. 83 kcal/mol for the Pd +? CH 2I bond. This figure is in agreement with an experimental bracket of 68 kcal/mol < BDE(Pd +? CH 2I) < 92 kcal/mol. Based on these findings, the previously studied Pd +/CH 3I system was re-investigated, and double-resonance experiments demonstrate that the formation of PdCH 2I + occurs stepwise via PdCH as a reactive intermediate. Further, ion/molecule reactions of PdCH 2I + with unsaturated hydrocarbons are studied, which reveal the formation of carbon–carbon bonds in the gas phase. 相似文献
8.
Third-order Møller–Plesset perturbation theory (MP 3) with a 6-31G** basis set was applied to study the relative stabilities of H +( X) 2 conformations ( X ? CO and N 2) and their clustering energies. The effect of both basis set extensions and electron correlation is not negligible on the relative stabilities of the H +(CO) 2 clusters. The most stable conformation of H +(CO) 2 is found to be a C∞v structure in which a carbon atom of CO bonds to the proton of H +(CO), whereas that of H +(N 2) 2 is a symmetry D∞h structure. The second lowest energy conformations of H +(CO) 2 and H +(N 2) 2 lie within 2 kcal/mol above the energies of the most stable structures. Clustering energies computed using MP 3 method with the 6-31G** basis set are in good agreement with the experimental findings of Hiraoka, Saluja, and Kebarle. The low-lying singlet conformations of H +( X) 3 ( X ? CO and N 2) have been studied by the use of the Hartree–Fock MO method with the 6-31G** basis set and second-order Møller–Plesset perturbation theory with a 4-31G basis set. The most stable structure is a T-shaped structure in which a carbon atom of CO (or a nitrogen atom of N 2) attacks the proton of the most stable conformation of H +( X) 2 clusters. 相似文献
9.
Ligand Site Preference in Iron Tetracarbonyl Complexes Fe(CO)4L (L = CO,CS, N2, NO+, CN–, NC–, η2‐C2H4, η2‐C2H2, CCH2, CH2, CF2, NH3, NF3, PH3, PF3, η2‐H2)
Equilibrium geometries, bond dissociation energies and relative energies of axial and equatorial iron tetracarbonyl complexes of the general type Fe(CO) 4L (L = CO, CS, N2, NO +, CN –, NC –, η 2‐C 2H 4, η 2‐C 2H 2, CCH 2, CH 2, CF 2, NH 3, NF 3, PH 3, PF 3, η 2‐H 2) are calculated in order to investigate whether or not the ligand site preference of these ligands correlates with the ratio of their σ‐donor/π‐acceptor capabilities. Using density functional theory and effective‐core potentials with a valence basis set of DZP quality for iron and a 6‐31G(d) all‐electron basis set for the other elements gives theoretically predicted structural parameters that are in very good agreement with previous results and available experimental data. Improved estimates for the (CO) 4Fe–L bond dissociation energies (D 0) are obtained using the CCSD(T)/II//B3LYP/II combination of theoretical methods. The strongest Fe–L bonds are found for complexes involving NO +, CN –, CH 2 and CCH 2 with bond dissociation energies of 105.1, 96.5, 87.4 and 83.8 kcal mol –1, respectively. These values decrease to 78.6, 64.3 and 64.2 kcal mol –1, respectively, for NC –, CF 2 and CS. The Fe(CO) 4L complexes with L = CO, η 2‐C 2H 4, η 2‐C 2H 2, NH 3, PH 3 and PF 3 have even smaller bond dissociation energies ranging from 45.2 to 37.3 kcal mol –1. Finally, the smallest bond dissociation energies of 23.5, 22.9 and 18.5 kcal mol –1, respectively are found for the ligands NF 3, N 2 and η 2‐H 2. A detailed examination of the (CO) 4Fe–L bond in terms of a semi‐quantitative Dewar‐Chatt‐Duncanson (DCD) model is presented on the basis of the CDA and NBO approach. The comparison of the relative energies between axial and equatorial isomers of the various Fe(CO) 4L complexes with the σ‐donor/π‐acceptor ratio of their respective ligands L thus does not generally support the classical picture of π‐accepting ligands preferring equatorial coordination sites and σ‐donors tending to coordinate in axial positions. In particular, this is shown by iron tetracarbonyl complexes with L = η 2‐C 2H 2, η 2‐C 2H 4, η 2‐H 2. Although these ligands are predicted by the CDA to be stronger σ‐donors than π‐acceptors, the equatorial isomers of these complexes are more stable than their axial pendants. 相似文献
10.
Nitridophosphates MP 2N 4:Eu 2+ (M=Ca, Sr, Ba) and BaSr 2P 6N 12:Eu 2+ have been synthesized at elevated pressures and 1100–1300 °C starting from the corresponding azides and P 3N 5 with EuCl 2 as dopant. Addition of NH 4Cl as mineralizer allowed for the growth of single crystals. This led to the successful structure elucidation of a highly condensed nitridophosphate from single‐crystal X‐ray diffraction data (CaP 2N 4:Eu 2+ ( P6 3, no. 173), a=16.847(2), c=7.8592(16) Å, V=1931.7(6) Å 3, Z=24, 2033 observed reflections, 176 refined parameters, wR2=0.096). Upon excitation by UV light, luminescence due to parity‐allowed 4f 6( 7F)5d 1→4f 7( 8S 7/2) transition was observed in the orange (CaP 2N 4:Eu 2+, λmax=575 nm), green (SrP 2N 4:Eu 2+, λmax=529 nm), and blue regions of the visible spectrum (BaSr 2P 6N 12:Eu 2+ and BaP 2N 4:Eu 2+, λmax=450 and 460 nm, respectively). Thus, the emission wavelength decreases with increasing ionic radius of the alkaline‐earth ions. The corresponding full width at half maximum values (2240–2460 cm ?1) are comparable to those of other known Eu 2+‐doped (oxo)nitrides emitting in the same region of the visible spectrum. Following recently described quaternary Ba 3P 5N 10Br:Eu 2+, this investigation represents the first report on the luminescence of Eu 2+‐doped ternary nitridophosphates. Similarly to nitridosilicates and related oxonitrides, Eu 2+‐doped nitridophosphates may have the potential to be further developed into efficient light‐emitting diode phosphors. 相似文献
11.
The MP2 and CCSD calculations of the geometries and binding energies of the Li+·(N2)n (n?=?1–4) complexes are obtained. The potential energy surface showed that these complexes exhibit one minimum state and one transition state. The mono- and di-ligated complexes exhibit linear configurations with a binding energy of 11.1 and 21.2 kcal mol?1, respectively. Trigonal planar and tetrahedral configurations are obtained for tri- and tetra-ligated complexes, respectively. The computed sequential bond dissociation energies (BDEs) of Li+·(N2)n (n?=?1–4) complexes are also calculated in which the mono-ligated complex has the largest BDE value. The obtained trend is mainly dependent on the variation in the ion-quadrupole interaction of these ion complexes. These calculations predict that these complexes are of purely electrostatic nature. 相似文献
12.
Cationic R 2P 5+ cage compounds ( 1 +) have been synthesized by the stoichiometric reaction of R 2PCl, GaCl 3 and P 4. The reaction conditions depend on the substituent R. Alkyl‐substituted derivatives ( 1 a – 1 d [GaCl 4]) are best synthesized under solvent‐free conditions, whereas aryl‐substituted derivatives ( 1 e – 1 h [GaCl 4]) are formed in C 6H 5F. All compounds have been prepared on a multi‐gram scale in good to excellent yields and have been fully characterized with an emphasis on 31P NMR spectroscopy in solution and single‐crystal structure determination. Subsequent chalcogenation reactions of cations R 2P 5+ ( 1 a +, 1 e +) and trication Ph 6P 73+ ( 3 3+) with elemental sulfur (α‐S 8) or grey selenium (Se grey) yielded a series of unique polyphosphorus–chalcogen cations ( 4 a +, 4 e +, 5 a +, 6 2+ and 7 2+), possessing nortricyclane‐type molecular structures. An in‐depth study of the 31P{ 1H} and 77Se NMR spectroscopic parameters is presented, and correlations between the substitution pattern and the observed structural features have been investigated in detail. 相似文献
13.
The reactions of Ru + with C 2H 6, C 3H 8, HC(CH 3) 3, and c-C 3H 6 at hyperthermal energies have been studied using guided ion beam mass spectrometry. It is found that dehydrogenation is efficient and the dominant process at low energies in all four reaction systems. At high energies, C-H cleavage processes dominate the product spectrum for the reactions of Ru + with ethane, propane, and isobutane. C-C bond cleavage is a dominant process in the cyclopropane system. The reactions of Ru + are compared with those of the first-row transition metal congener Fe + and the differences in behavior and mechanism are discussed in some detail. Modeling of the endothermic reaction cross sections yields the 0-K bond dissociation energies (in eV) of D 0(Ru-H)=2.27±0.15, D 0(Ru +-C)=4.70±0.11, D 0(Ru +-CH)=5.20±0.12, D 0(Ru +-CH 2)=3.57±0.05, D 0(Ru +-CH 3)=1.66±0.06, D 0(Ru-CH 3)=1.68±0.12, D 0(Ru +-C 2H 2)=1.98±0.18, D 0(Ru +-C 2H 3)=3.03±0.07, and D 0(Ru +-C 3H 4)=2.24±0.12. Speculative bond energies for Ru +=CCH 2 of 3.39±0.19 eV and Ru +=CHCH 3 of 3.19±0.15 eV are also obtained. The observation of exothermic processes sets lower limits for the bond energies of Ru + to ethene, propene, and isobutene of 1.34, 1.22, and 1.14 eV, respectively. 相似文献
14.
The complexation properties of the open-chain N 2S 2 ligands 1–4 are described and compared to those of analogous N 2S 2 macrocycles 5–7 . With Cu 2+, the open-chain ligands give complexes with the stoichiometry CuL 2+ and CuLOH +, the stabilities and absorption spectra of which have been determined. The ligand field exerted by these ligands is relatively constant and independent of the length of the chain. With Cu +, the species CuLH, CuLH 2+, and CuL + were identified and their stabilities measured. The redox potentials calculated from the equilibrium constants and measured by cyclic voltammetry agree and lie between 250 and 280 mV against SHE. The comparison between open-chain and cyclic ligands shows that ( 1) a macrocyclic effect is found for Cu 2+ but not for Cu +, ( 2) the ligand-field strength is very different for the two types of ligands, and ( 3) the redox potentials span a larger interval for the macrocyclic than for the open-chain complexes. 相似文献
15.
The structures and energies of B +13, observed experimentally to be an unusually abundant species among cationic boron clusters, have been studied systematically with B3LYP/6–31G* density functional theory. The most thermodynamically stable B +12 and B +13 clusters are confirmed to have planar or quasiplanar rather than globular structures. However, the computed dissociation energies of the 3-dimensional B +13 clusters are much closer to the experimental values than those of the planar or quasiplanar structures. Hence, planar and 3-dimensional B +13 may both exist. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 203–214, 1998 相似文献
16.
Mass-selected beams of N + and N 2+ in the energy range 5–50 eV react with molybdenum to produce a surface nitride. The relative reaction cross section for N + reaction is higher than that of N 2+ in the range 5–25 eV and N 2+ exhibits a reaction threshold near 7 eV. The N 2+ threshold suggests collisional dissociation prior to reaction. 相似文献
17.
A density functional theory study on the geometrical structures and dissociation channels of MP
n
+ (M = Fe, Co or Ni; n = 2, 4, 6 or 8) binary cluster ions has been performed. The tetrahedral P 4 structure and linear P 2 structure are found to be two relatively stable units in these ions. The lowest energy structures of MP
n
+ cluster ions are constructed by bonding a twofold or fourfold M atom with a P 4 or P 2 unit. The M–P bond is clearly weaker than the P–P bond. The most likely dissociation channel of the MP
n
+ cluster ions is the detachment of a P 4 or P 2 fragment. This conclusion is well consistent with the published experimental data and consistent with our previously reported
theoretical study on the CrP
m
+ ( m = 2, 4, 6 or 8) cluster ions. 相似文献
18.
The most stable conformation of ion-molecule complexes involving a CO molecule were surveyed by the use of Hartree-Fock (HF) MO and third-order Moller-Plesset perturbation (MP3) methods with a 6–31G* basis set ion = H +, Li +, Na +, K +, Bc 2+, Mg 2+, and Ca 2+. The MP3 level of theory reveals the ion-CO conformation in which the ion bonds to a carbon atom of CO to be the most stable; these MP3 results are contrary to the HF ones. Binding energies of ion-molecule complexes involving CO and N 2 were computed; MP3 energies are in good agreement with the experimental ones. The computed binding energies of cation-N 2 are about one-third of cation-NH 3 due to the absence of dipole moment and the smaller polarizability of N 2. The decrease in binding energy in cation-CO and -N 2 complexes, with increasing cation size, is mainly caused by the decrease of the electrostatic and polarization stabilizations. 相似文献
19.
Photoionisation mass spectrometry was used to obtain the fragmentation pathways of pyridine, pyridazine, pyrimidine, pyrazine and s-triazine molecules upon absorption of 23.0, 15.7 and 13.8 eV synchrotron photons. The ionic fragments observed vary from molecule to molecule, however C 2H 2+, HCN +and HCNH + are common to all five molecules at the three photon energies. Furthermore, the presence of C 2H 2N 2+, C 3H 3N + and C 4H 4+ in the spectra of some of the molecules suggests dissociation pathways via loss of HCN moieties. The respective parent cations, m/ q=79, 80 and 81 have a greater yield at low photon energies when compared to the most intense fragment peak in each spectra. We recorded two of the fragment cation yields, as well as the parent photoion yield curves of pyridine, pyridazine, and pyrimidine in the 8–30 eV range. The formation of abundant cation fragments show a strong propensity of the molecules for dissociation after the absorption of VUV photons higher than 14 eV. The differences in relative fragment yields from molecule to molecule, and when changing the excitation energy, suggest significant bond rearrangements and nuclear motion during the dissociation time. Thus, bond cleavage is dependent on the photon energy deposited in the molecule and on intramolecular reactivity. With the aid of photoion yield curves and energy estimations we have assigned major peaks in the spectra and discussed their fragmentation pathways. 相似文献
20.
The unimolecular chemistry and structures of self‐assembled complexes containing multiple alkaline‐earth‐metal dications and deprotonated GlyGly ligands are investigated. Singly and doubly charged ions [M n(GlyGly?H) n‐1] + ( n=2–4), [M n+1(GlyGly?H) 2n] 2+ ( n=2,4,6), and [M(GlyGly?H)GlyGly] + were observed. The losses of 132 Da (GlyGly) and 57 Da (determined to be aminoketene) were the major dissociation pathways for singly charged ions. Doubly charged Mg 2+ clusters mainly lost GlyGly, whereas those containing Ca 2+ or Sr 2+ also underwent charge separation. Except for charge separation, no loss of metal cations was observed. Infrared multiple photon dissociation spectra were the most consistent with the computed IR spectra for the lowest energy structures, in which deprotonation occurs at the carboxyl acid groups and all amide and carboxylate oxygen atoms are complexed to the metal cations. The N?H stretch band, observed at 3350 cm ?1, is indicative of hydrogen bonding between the amine nitrogen atoms and the amide hydrogen atom. This study represents the first into large self‐assembled multimetallic complexes bound by peptide ligands. 相似文献
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