A simple interpretation of the Fe2(-) photoelectron spectrum

The photoelectron spectrum of Fe2(-) can be simply interpreted in terms of electron detachment from the mildly bonding 4s sigma sup * sub u orbital of a (4s sigma sub s)(sup 2) (4s sigma sup * sub u)(sup 2) (3d)(sup 13) anion. This interpretation implies a (4s sigma sub g)(sup 2) (4s sigma sup * sub u)(sup1) (3d)(sup13) configuration for the ground state of Fe2, correlating with one ground state (4s2 3d6) and one excited state (4s1 3d7) Fe atom. A comparison of the bond length and vibrational frequency of Fe2 to values for transition metal dimers containing single 4s-4s bonds is suggestive of 3d-3d bonding in this molecule. The results of preliminary full-valence configuration interaction calculations provide stron support for the proposed Fe2 and Fe2(-) configurations

Mistletoe lectin is not the only cytotoxic component in fermented preparations of Viscum album from white fir (Abies pectinata)

<p>Abstract</p> <p>Background</p> <p>Preparations of mistletoe (<it>Viscum album</it>) are the form of cancer treatment that is most frequently used in the complementary medicine. Previous work has shown that these preparations are able to exert cytotoxic effects on carcinoma cells, the extent of which might be influenced by the host tree species and by the content of mistletoe lectin.</p> <p>Methods</p> <p>Using colorimetric assays, we have now compared the cytotoxic effects of <it>Viscum album </it>preparations (VAPs) obtained from mistletoe growing on oak (<it>Quercus robur </it>and <it>Q. petraea</it>, VAP-Qu), apple tree (<it>Malus domestica</it>,, VAP-M), pine (<it>Pinus sylvestris</it>, VAP-P) or white fir (<it>Abies pectinata</it>, VAP-A), on the <it>in vitro </it>growth of breast and bladder carcinoma cell lines. While MFM-223, KPL-1, MCF-7 and HCC-1937 were the breast carcinoma cell lines chosen, the panel of tested bladder carcinoma cells comprised the T-24, TCC-SUP, UM-UC-3 and J-82 cell lines.</p> <p>Results</p> <p>Each of the VAPs inhibited cell growth, but the extent of this inhibition differed with the preparation and with the cell line. The concentrations of VAP-Qu, VAP-M and VAP-A which led to a 50 % reduction of cell growth (IC₅₀) varied between 0.6 and 0.03 mg/ml. Higher concentrations of VAP-P were required to obtain a comparable effect. Purified mistletoe lectin I (MLI) led to an inhibition of breast carcinoma cell growth at concentrations lower than those of VAPs, but the sensitivity towards purified MLI did not parallel that towards VAPs. Bladder carcinoma cells were in most cases more sensitive to VAPs treatment than breast carcinoma cells. The total mistletoe lectin content was very high in VAP-Qu (54 ng/mg extract), intermediate in VAP-M (25 ng/mg extract), and very low in VAP-P (1.3 ng/mg extract) and in VAP-A (1 ng/mg extract). As to be expected from the low content of mistletoe lectin, VAP-P led to relatively weak cytotoxic effects. Most remarkably, however, the lectin-poor VAP-A revealed a cytotoxic effect comparable to, or even stronger than, that of the lectin-rich VAP-Qu, on all tested bladder and breast carcinoma cell lines.</p> <p>Conclusion</p> <p>The results suggest the existence of cytotoxic components other than mistletoe lectin in VAP-A and reveal an unexpected potential of this preparation for the treatment of breast and bladder cancer.</p

A STUDY OF NbMo AND NbMo−^{-} BY ANION PHOTOELECTRON SPECTROSCOPY

Author Institution: Department of Chemistry, University of Minnesota, Minneapolis, MN 55455We report the 488 and 514 nm anion photoelectron spectra of NbMo$^{-}$. R2PI spectroscopic studies have established that neutral NbMo has a $^{2}\Delta_{5/2}$ ground state and a short bond length . We find that the NbMo$^{-}$ anion has a $^{1}\Sigma^{+}$ ground state in which the "extra" electron occupies the (4d)$\delta$ bonding orbital, giving a $1\sigma^{2}1\pi^{4}1\delta^{4}2\sigma^{2}$ valence electron configuration. Thus, NbMo$^{-}$ has a formal bond order of 6, and is isoelectronic with Mo$_2$. Low-lying excited states of NbMo ($^{2}\Sigma^{+}$) and NbMo$^{-}$ ($^{3}\Delta$) are also observed. The spectra provide the electron affinity of NbMo, energies of the $^{2}\Sigma^{+}$ and $^{3}\Delta$ excited states, vibrational frequencies in the anion and neutral molecule ground states and the $^{2}\Sigma^{+}$ state, $^{2}\Delta$ and $^{3}\Delta$ spin-orbit splittings, and (from Franck-Condon analyses) bond length measurements for the anion ground state and the observed excited states. These results are compared with previous anion photoelectron spectroscopic data for the Group 5/6 congeners VCr and VMo, and with density functional theory predictions

A STUDY OF NbCr AND NbCr−^{-} BY ANION PHOTOELECTRON SPECTROSCOPY

Author Institution: Department of Chemistry, University of Minnesota, Minneapolis, MN 55455We report the 488 nm photoelectron spectrum of the NbCr$^{-}$ anion. For the $^{2}\Delta$ ground state of neutral NbCr, the short bond length (1.894 \AA) and high bond energy (D$_0$ 3.0263(6) eV) measured by R2PI spectroscopy indicate high order multiple bonding. We find that the NbCr$^{-}$ anion has a $^{1}\Sigma^{+}$ ground state, in which the "extra" electron occupies the (4d)$\delta$ bonding orbital, giving a $1\sigma^{2}1\pi^{4}1\delta^{4}2\sigma^{2}$ valence electron configuration and a formal bond order of 6. Low-lying excited states of NbCr (assigned as two $^{2}\Sigma^{+}$ states) and NbCr$^{-}$ ($^{3}\Delta$) are also observed. The spectra provide the electron affinity of NbCr, energies of the $^{2}\Sigma^{+}$ and the $^{3}\Delta$ excited states, vibrational frequencies for the NbCr and NbCr$^{-}$ ground states and for the $^{2}\Sigma^{+}$ excited states, and (from Franck-Condon analyses) differences among the bond lengths of the observed states. These results are compared with our previous data for the Group 5/6 congeners NbMo, VCr, and VMo, and with DFT predictions. We also report results for ongoing experiments on the flow tube reactions of the Group V metals Nb and Ta with butadiene, and the vibrationally-resolved photoelectron spectra of some of the organometallic reaction product anions

A NEGATIVE ION PHOTOELECTRON SPECTROSCOPIC AND COMPUTATIONAL STUDY OF CrV AND MoV

Author Institution: Department of Chemistry, University of Minnesota; Minneapolis, MN 55455The heteronuclear diatomic metal ions CrV$^{-}$ and MoV$^{-}$ were investigated using negative ion photoelectron spectroscopy. These bare, heteronuclear group 5 and 6 transition metal dimers allow the study of multiple metal-metal bonding free of ligand effects. The photoelectron spectra, obtained at 488 nm with an instrumental resolution of about 5 meV (40 cm$^{-1}$), provide measurements of the electron affinities, vibrational frequencies for both the anion and neutral states, bond length changes upon electron detachment, excited electronic state energies and spin-orbit splittings. The CrV$^{-}$ and MoV$^{-}$ spectra display transitions to the multiply-bonded $^{2}\Delta$ $(d\pi)^{4}(d\delta)^{3}(d\sigma)^{2}(s\sigma)^{2}$ ground states of the neutral molecules and to several excited states. Addition of an electron to the vacant $\sigma^{*}$ orbital gives the $^{3}\Delta$ anion, which is found to be the ground state of CrV$^{-}$ but a low lying excited state of MoV$^{-}$. Addition of a d$\delta$ electron yields the $^{1}\Sigma^{+}$ MoV$^{-}$ ground state. Density functional theory calculations of the anions and neutrals were performed to help elucidate the spectroscopic assignments and observed periodic trends

A NEGATIVE ION PHOTOELECTRON SPECTROSCOPIC AND COMPUTATIONAL STUDY OF Mo2_{2} AND Mo2−_{2}^{-}

Author Institution: Department of Chemistry, University of Minnesota, Minneapolis, MN 55455We report the 488 and 514 nm anion photoelectron spectra of Mo$_{2}^{-}$. Neutral Mo$_{2}$ has been described in recent $ab$ $initio$ studies as having a bond order of six, predicted to be the highest of any homonuclear diatomic, exceeding even that of Cr$_{2}$(five). The photoelectron spectrum of Mo$_{2}^{-}$confirms the previously measured vibrational frequency of gas phase Mo$_{2}$ and displays transitions to vibrational levels up to v=7 in its $^{1}\Sigma_{g}^{+}$ ground state. The electron affinity of Mo$_{2}$ is measured to be 0.732 $\pm$ 0.010 eV. The Mo$_{2}^{-}$ ground state is assigned as a $^{2}\Sigma_{u}^{+}$ state, in which the extra electron occupies a formally antibonding $\sigma_{u}$ orbital of primarily 5$s$ atomic parentage. A Franck-Condon analysis of the vibrational band intensities indicates a change in the equilibrium bond length of only 0.03 $\pm$ 0.02 \AA $$ upon electron detachment. These results, and the similar vibrational frequencies measured for Mo$_{2}$ and Mo$_{2}^{-}$, suggest that the anion HOMO is essentially nonbonding. Weak photodetachment transitions to excited states of Mo$_{2}$ lying within 1.2 eV of its ground state are also observed. DFT calculations using the BPW91/SDD method show good agreement with experiment for the electron affinity of Mo$_{2}$ and the bond lengths in the anion and neutral molecule ground states. It is hoped that these spectroscopic results will motivate and assist high level theoretical studies of the Mo$_{2}^{-}$ anion

Photoelectron spectroscopy of the halocarbene anions HCF\u3csup\u3e-\u3c/sup\u3e, HCCl\u3csup\u3e-\u3c/sup\u3e, HCBr\u3csup\u3e-\u3c/sup\u3e, HCl\u3csup\u3e-\u3c/sup\u3e, CF\u3csub\u3e2\u3c/sub\u3e\u3csup\u3e-\u3c/sup\u3e, and CCl\u3csub\u3e2\u3c/sub\u3e\u3csup\u3e-\u3c/sup\u3e

The 488 nm photoelectron spectra are reported for the HCX(X̃ 1A′) + e-←HCX-(X̃ 2A″) and HCX(ã3A″) + e -←HCX-(X̃2A″) transitions in HCF-, DCF-, HCCl-, HCBr-, and MCI- and for the CX2(X̃1A1) + e-←CX2- (X̃2B1) transitions in CF2- and CCl2-. Adiabatic electron affinities are found to be 0.557 ± 0.005 eV (HCF), 0.552 ± 0.005 eV (DCF), 1.213 ± 0.005 eV (HCCl), 1.556 ± 0.008 eV (HCBr), 1.683 ± 0.012 eV (HCI), 0.179 ± 0.005 eV (CF 2), and 1.603 ± 0.008 eV (CCl2). Bounds for the triplet excitation energies are determined for all the halocarbenes for which photoelectron spectra were observed, with the exception of CCl2. For the HCX halocarbenes, upper bounds for the triplet excitation energies are 14.7 ± 0.2 kcal/mol (HCF, DCF), 11.4 ± 0.3 kcal/mol (HCCl), and 9 ± 2 kcal/mol (HCBr). A more detailed analysis of HCF suggests the actual triplet excitation energy to be 11.4 ± 0.3 kcal/mol, 14.7 ± 0.2 kcal/mol, or 8.1 ± 0.4 kcal/mol, with the first value the most likely. Since the multiplicity of the ground state of HCl is not known, we report the energy of its first excited state to be less than 9 ± 2 kcal/mol. The absence of an observed triplet state in the CF2- photoelectron spectrum allows us to assign a lower bound on the triplet excitation energy of CF2 of 50 ± 2 kcal/mol. © 1988 American Institute of Physics

Methylene: A study of the X̃\u3csup\u3e3\u3c/sup\u3eB\u3csub\u3e1\u3c/sub\u3e and ã\u3csup\u3e1\u3c/sup\u3eA\u3csub\u3e1\u3c/sub\u3e states by photoelectron spectroscopy of CH \u3csub\u3e2\u3c/sub\u3e\u3csup\u3e-\u3c/sup\u3e and CD\u3csub\u3e2\u3c/sub\u3e\u3csup\u3e-\u3c/sup\u3e

Photoelectron spectra are reported for the CH2(X̃ 3B1) + e-←CH2- (X̃2B1) and CH2(ã1A 1) + e-←CH2-(X̃2B1) transitions of the methylene and perdeuterated methylene anions, using a new flowing afterglow photoelectron spectrometer with improved energy resolution (11 meV). Rotational relaxation of the ions to ∼300 K and partial vibrational relaxation to \u3c 1000 K in the flowing afterglow negative ion source reveal richly structured photoelectron spectra. Detailed rotational band contour analyses yield an electron affinity of 0.652±0.006 eV and a singlet-triplet splitting of 9.00±0.09 kcal/mol for CH2. (See also the following paper by Bunker and Sears.) For CD2, results give an electron affinity of 0.645±0.006 eV and a singlet-triplet splitting of 8.98±0.09 kcal/mol. Deuterium shifts suggest a zero point vibrational contribution of 0.27±0.40 kcal/mol to the observed singlet-triplet splitting, implying a Te value of 8.7±0.5 kcal/mol. Vibrational and partially resolved rotational structure is observed up to ∼9000 cm-1 above the zero point vibrational level of the 3B1 states, revealing a previously unexplored region of the quasilinear potential surface of triplet methylene. Approximately 20 new vibration-rotation energy levels for CH2 and CD2 are measured to a precision of ∼30 cm-1 in the v2 = 2-7 region (bent molecule numbering). Bending vibrational frequencies in the methylene anions are determined to be 1230±30 cm-1 for CH 2- and 940±30 cm-1 for CD 2-, and the ion equilibrium geometries are bracketed. The measured electron affinity also provides values for the bond strength and heat of formation of CH2-, and the gas phase acidity of CH 3. A detailed description of the new flowing afterglow photoelectron spectrometer is given. © 1985 American Institute of Physics

Electron affinities of the alkali halides and the structure of their negative ions

Photoelectron spectra are reported for the MX (X̃ 1∑ +) + e-←MX-(X̃ 2∑ +) transitions often alkali halide anions at 488 nm. Adiabatic electron affinities (±0.010 eV) are determined to be 0.593 (LiCl), 0.520 (NaF), 0.727 (NaCl), 0.788 (NaBr), 0.865 (NaI), 0.582 (KCl), 0.642 (KBr), 0.728 (KI), 0.543 (RbCl), and 0.455 eV (CsCl). Fundamental vibrational frequencies, equilibrium bond lengths, and dissociation energies are also reported for the anion 2Σ+ ground states. An observed linear correlation of electron affinities with α/r2 (α = metal atom polarizability) is used to predict the electron affinities of the remaining alkali bromides and iodides, as well as related alkali salts. A simple electrostatic model for the alkali halide anions is also presented which enables the accurate (±0.1 eV) calculation of electron affinities. © 1986 American Institute of Physics