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Copper-diammonia, Cu(NH3)2, and its deuterated species, Cu(ND3)2, are produced in supersonic molecular beams and studied by pulsed-field ionization zero electron kinetic energy photoelectron spectroscopy and ab initio calculations. Structural isomers with a copper atom binding to an ammonia dimer or two ammonia molecules are obtained by the calculations. By comparing the experimental measurements to the theoretical calculations, the neutral and ionic forms of copper-diammonia are determined to be in a doubly bound linear conformation in their ground electronic states. The adiabatic ionization potentials of Cu(NH3)2 and Cu(ND3)2 are measured as 29 532 (5) and 29 313 (5) cm-1, respectively. The metal-ligand symmetric stretching frequencies are measured to be 436 cm-1 for Cu+–(NH3)2 and 398 cm-1 for Cu+–(ND3)2, and the metal-ligand bending frequencies 75/139 cm-1 for Cu/Cu+–(NH3)2 and 70/125 cm-1 for Cu/Cu+–(ND3)2. Moreover, the dissociation energy of Cu(NH3)2→CuNH3+NH3 is determined to be 11(3) kcal mol-1 through a thermodynamic relationship. [ABSTRACT FROM AUTHOR]

Vibrational frequencies of three niobium normal modes of triniobium dicarbide neutral and cation have been determined from pulsed field ionization-zero electron kinetic energy photoelectron spectra. The niobium stretching mode has a frequency of 326 cm[SUP-1]in the neutral and 339 cm[SUP-1]in the ion. The two deformation modes have frequencies of 238 and 82 cm[SUP-1]in the neutral and a degenerate frequency of 258 cm[SUP-1]in the ion. The geometry of the triniobium dicarbide has been established by comparing the experimental spectra with theoretical calculations. The cluster has a trigonal bipyramid geometry with carbon atoms capping on each face of the metal frame. The cation cluster has D[SUB3h] symmetry whereas the neutral cluster has lower symmetry resulting from a Jahn-Teller distortion. A second low-lying structure with doubly bridging carbon atoms has been identified by the calculations but has not yet been observed. [ABSTRACT FROM AUTHOR]

The geometrical structures of the ground states of triniobium monoxide, Nb3O, and its cation, Nb3O+, have been determined by an experimental and theoretical study. Vibrationally resolved photoelectron spectra of an Nb3O cluster beam were obtained at 100 and 300 K using the pulsed field ionization-zero electron kinetic energy technique. The spectra were simulated by calculating multidimensional Franck–Condon factors using the geometries and harmonic vibrational frequencies obtained from density functional theory for the minimum energy structures of the ion and neutral molecule. The rather remarkable agreement between the experiment and the simulated spectra establishes that Nb3O and Nb3O+ have planar C2v structures with the oxygen atom bridging two niobium atoms. These are the most complex transition metal cluster structures to date to be characterized by gas phase spectroscopic techniques. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

La atom reactions with 1-butene, 2-butene, and isobutene are carried out in a laser-vaporization molecular beam source. The three reactions yield the same La-hydrocarbon products from the dehydrogenation and carbon-carbon bond cleavage and coupling of the butenes. The dehydrogenated species La(C4H6) is the major product, which is characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectrum of La(C4H6) produced from the La+1-butene reaction exhibits two band systems, whereas the MATI spectra produced from the La+2-butene and isobutene reactions display only a single band system. Each of these spectra shows a strong origin band and several vibrational progressions. The two band systems from the spectrum of the 1-butene reaction are assigned to the ionization of two isomers: La[C(CH2)3] (Iso A) and La(CH2CHCHCH2) (Iso B), and the single band system from the spectra of the 2-butene and isobutene reactions is attributed to Iso B and Iso A, respectively. The ground electronic states are 2A1 (C3v) for Iso A and 2A′ (Cs) for Iso B. The ionization of the doublet state of each isomer removes a La 6s-based electron and leads to the 1A1 ion of Iso A and the 1A′ ion of Iso B. The formation of both isomers consists of La addition to the C=C double bond, La insertion into two C(sp3)—H bonds, and H2 elimination. In addition to these steps, the formation of Iso A from the La+1-butene reaction may involve the isomerization of 1-butene to isobutene prior to the C—H bond activation, whereas the formation of Iso B from the La+trans-2-butene reaction may include the trans- to cis-butene isomerization after the C—H bond activation. [ABSTRACT FROM AUTHOR]

The vibrational structure of the Ag+NH3 complex has been investigated by single-photon zero kinetic energy (ZEKE) photoelectron spectroscopy. The intermolecular stretching mode with a frequency of 375 cm−1 is measured from the ZEKE spectrum, whereas the intermolecular bending vibration is not observed, in contrast to the A˜2E1/2–X˜2A1 electronic spectrum of the neutral AgNH3 complex [Miyawaki et al., Chem. Phys. Lett. 302 (1999) 354]. The ionization potential of AgNH3 was determined to be 47580 cm−1 (5.899 eV). [Copyright &y& Elsevier]

LaO2 was produced in a pulsed laser-vaporization molecular beam source and studied by mass-analyzed threshold ionization (MATI) spectroscopy and ab initio electronic structure calculations. The calculations included density functional theory, second-order perturbation theory, coupled cluster theory, and complete active space self-consistent field methods. The adiabatic ionization energy of the molecule and vibrational frequencies of the molecule and its cation were measured accurately for the first time from the MATI spectrum. Numerous ionization processes of lanthanum dioxide, peroxide, and superoxide were considered; the 3B2 ← 4B2 electronic transition of the dioxide was assigned upon comparison with the observed spectrum. The ionization energy and O-La-O bending frequency of the 4B2 neutral state are 4.9760 (6) eV and 92 cm-1, respectively. The La-O stretching and O-La-O bending frequencies of the 3B2 cationic state are 656 and 122 cm-1, respectively. The 4B2 state is formed by two electron transfer from lanthanum to oxygen atoms, and the 3B2 state is produced by the further removal of a lanthanum 6s-based electron. [ABSTRACT FROM AUTHOR]

Single-photon pulsed field ionization-zero electron kinetic energy photoelectron spectroscopy has been used to study the indium–methylamine complexes. The photoelectron spectra have been assigned using density functional theory and Franck–Condon calculations. The spectral assignments identify the symmetric In[sup +]–N stretch mode for In[sup +]–NH[sub 2]CH[sub 3] (259 cm-1), In[sup +]–NH(CH[sub 3])[sub 2] (200 cm-1), and In[sup +]–N(CH[sub 3])[sub 3] (158 cm-1); In–N stretch for In–N(CH[sub 3])[sub 3] (110 cm-1); In[sup +]–N–C bend for In[sup +]–NH[sub 2]CH[sub 3] (110 cm-1) and In[sup +]–NH(CH[sub 3])[sub 2] (120 cm-1); In–N–C bend for In–NH[sub 2]CH[sub 3] (91 cm-1) and In–NH(CH[sub 3])[sub 2] (106 cm-1); and In[sup +]–N–H bend for In[sup +]–NH(CH[sub 3])[sub 2] (324 cm-1). Methyl substitutions for hydrogen atoms greatly influence the indium–nitrogen stretch forces and ionization potentials of the complexes. The indium–amine binding in these complexes includes orbital interaction and electrostatic forces. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Threshold ionization spectra of nozzle-jet cooled tetrakis(dimethylamino)ethylene (TDAE) were measured with high-resolution electron and laser ionization techniques, and Raman spectra of the molecule at room temperature and under liquid nitrogen were recorded with laser excitation. The TDAE ion signal shows a gradual increase at the onset of ionization, and the upper bounds of the adiabatic ionization potential (IP) measured from the electron ionization and laser ionization are 5.3±0.2 and 5.20±0.05eV, respectively. In combination with the experimental measurements, density functional theory calculations were used to predict the adiabatic and vertical IPs and vibrational frequencies. The predicted adiabatic IP (5.2eV) and Cing frequency (1622cm−1) are in excellent agreement with the measured values. The adiabatic IP is about 0.6eV lower than the vertical IP (5.8eV). The large difference between the adiabatic and vertical IPs arise from the significant geometry change upon ionization and is consistent with the experimental observation of the slowly rising ion signal at the ionization onset of the molecule in both the electron ionization and photoionization experiments. Raman spectroscopy of TDAE at room temperature and at liquid nitrogen (Raman under nitrogen, RUN) is reported in an attempt at examining higher energy conformers. [Copyright &y& Elsevier]