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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 102 (1980), S. 7702-7709 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2535-2543 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fluorescence excitation and emission spectra of the van der Waals molecules InAr, InKr, and InXe, formed by laser vaporization of a metal target followed by supersonic expansion, have been recorded. Observed vibrational progressions indicate that the interatomic potentials for the X 2Π1/2,3/2 and B 2Σ+ states can be approximated by Morse functions. Isotopic splittings are observed in the excitation spectra and allow the vibrational numbering in the excited B 2Σ+ state to be assigned. The dissociation energies of the three states are estimated for each molecule and are found to correlate well with the rare gas polarizabilities.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1899-1904 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The diatomic molecule ZrS has been observed by laser induced fluorescence in a supersonic molecular beam following reaction of laser-vaporized zirconium atoms with (approximate)2% carbonyl sulfide (OCS) added into a flow of He carrier gas. Two band systems have been observed in the 413–700 nm region. The R heads of their band origins lie at 20 218.9 and 20 208.3 cm−1. The former is tentatively ascribed to the E 1Σ+–X 1Σ+ transition; the latter remains unassigned but is shown to borrow all of its intensity from the former through a simple intensity borrowing mechanism. A vibrational analysis leads to the following molecular constants for the ground state: ωe=548.4 cm−1, ωexe=1.6 cm−1. Franck–Condon factors for several vibronic transitions are also reported. Intrinsic radiative lifetimes of several vibrational levels of both upper states have been measured, and confirm that the two states perturb each other. A limited deperturbation analysis has been carried out. Vibrational constants, mixing coefficients, interaction matrix elements, and other spectroscopic parameters are reported.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 5252-5261 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Interatomic potential parameters for the ground X1,2 2Π1/2,3/2 and excited B 2Σ+1/2 states of jet-cooled van der Waals complexes of Al atoms with rare gases have been determined from fluorescence excitation and emission spectra. Vibrational numbering in the B states is established from isotopic and rotational broadening of fluorescence excitation line shapes. Bond distances are estimated by comparison with analogous states of alkali–rare gas molecules, and by modeling observed relative emission intensities with calculated Franck–Condon factors. Morse potentials are found to adequately describe the data for the ground states, but for the excited states there are indications of departures from Morse functions at large internuclear distances. Dissociation energies De are estimated from Birge–Sponer extrapolations. Multiplet splittings in Al–rare gas complexes are compared to those in In–rare gas complexes and are discussed in terms of an empirical treatment of spin–orbit coupling, which assumes that the spin–orbit coupling constant for the molecule is the same as that for the atom. The ground X1 state of each Al–rare gas molecule is more stable than that of the analogous In complex, whereas the spin–orbit excited X2 state is less stable. This is explained by the greater mixing between the X1 state and the dissociative A 2Σ+1/2 state for indium over aluminum, caused by the greater spin–orbit coupling constant for the heavier metal.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7822-7829 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reactivity of ground state iron atoms with respect to atom transfer and adduct formation reactions with a variety of simple molecules in Ar buffer gas near room temperature has been investigated. Iron atoms are produced by visible multiphoton dissociation of iron pentacarbonyl or ferrocene, and their removal by added gases under pseudo-first-order conditions is monitored by resonance fluorescence excitation at variable time delay following the photolysis pulse. Upper limits for second-order rate constants for reaction of ground state iron atoms with O2, CO, H2O, (CH3)2O, C2H2, C2H4, N2O, C2H4O, and CF3Cl at room temperature and 100 Torr total pressure are estimated to be in the range (2–10)× 10−15 cm3 molecule−1 s−1, which corresponds to reaction probabilities of less than (approximately-equal-to)10−5 per hard sphere collision. Pseudo-second-order rate constants in the range (2–60)× 10−14 cm3 molecule−1 s−1 are found for 1:1 adduct formation reactions of ground state iron atoms with C6H6, 1,3-butadiene, NH3, and NO. The formation of such complexes at room temperature implies that the binding energies are greater than (approximately-equal-to)7 kcal mol−1.For the complex FeNH3, the kinetic data allow measurements of dissociation equilibrium constants at 278.5 and 295 K, from which a binding energy ΔH°0 = 7.5 ± 1 kcal mol−1 is derived. Measurements of the dependence of the pseudo-second-order rate constant for formation of FeNO on the pressure of Ar buffer gas at 296 K allow estimates to be made of the limiting low- and high-pressure recombination rate constants: k0 =2.3×10−32 cm6 molecule−2 s−1 and k∞=1×10−12 cm3 molecule−1 s−1. Comparisons are made between the present results which indicate a remarkably low reactivity for iron atoms, and previously reported results for reactions of iron atoms in low temperature matrices and gas phase reactions of other transition metal atoms. An interpretation of our results is given in terms of schematic potential energy curves which are based on the results of previous ab initio calculations for the complex FeCO. The qualitative features of these curves are consistent with low reactivity of ground state iron atoms with respect to adduct formation due to repulsive ground state interactions and low probabilities for transitions from repulsive to attractive potential surfaces.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7813-7821 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ground state (a 5D) and metastable excited state (a 5F and a 3F) iron atoms have been produced by visible multiphoton dissociation of Fe(CO)5 at 552 nm in a static pressure gas cell at room temperature. The distribution of iron atoms among these states has been measured by using a pump and probe arrangement in which the probe laser pulse excites resonance fluorescence from iron atoms at variable time delay following the photolysis pulse. Collisional relaxation processes of metastable a 5F and a 3F iron atoms have been investigated by using a simple model to describe the main features of the overall relaxation process. Results for a variety of quenching gases including N2O, C2H4O, and O2 indicate that relaxation occurs mainly by transitions between adjacent multiplets, with little intermediate intramultiplet relaxation and no detectable removal by chemical reaction. An interpretation of these results is given in terms of schematic potential energy curves which represent the bonding capabilities of specific electronic configurations of iron atoms. These curves are discussed in an accompanying paper on studies of chemical reactions of ground state iron atoms.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 3194-3197 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An accurate value for the first ionization potential of zirconium of 53 506.0(3) cm−1 has been obtained from convergence limits of high lying Rydberg series observed using two laser, field- ionization spectroscopy of an atomic beam of zirconium. The new value is consistent with analysis of s-electron binding energies of other second transition series elements.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 5028-5042 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: UV and visible multiphoton dissociation (MPD) processes of Ga(CH3)3 have been investigated by time-resolved detection of Ga(4 2PJ ) (J=1/2, 3/2) and Ga(5 2S1/2) following pulsed laser photolysis in a low pressure gas cell, and by mass spectrometric detection of ionic photofragments in a molecular beam. The relative abundances of neutral and ionic fragments were monitored as a function of photolysis wavelength and flux. Measurements of the anisotropy of the velocity distribution and the average kinetic energy of nascent Ga(4 2PJ ) are also reported. Under conditions of moderate photolysis flux ((approximately-equal-to)108 W cm−2), MPD of Ga(CH3)3 in the wavelength range 420–520 nm produced mainly neutral fragments, including Ga(4 2PJ ) and a metastable molecular fragment which is identified as GaCH3. Photolysis at 222 nm produced GaCH3 to the exclusion of Ga(4 2PJ ), or primarily ionic fragments at relatively high flux. At 308 nm, ionic Ga(CH3)+n species were produced in relatively high yield even in the limit of low photolysis flux. The mechanisms of MPD and MPI of Ga(CH3)3 are discussed with reference to simple rate equations models.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5539-5547 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Reactions of molybdenum clusters with molecular nitrogen have been investigated by using a fast-flow reactor equipped with a laser vaporization cluster source and laser ionization time-of-flight mass spectrometer for detection of clusters. Absolute rate coefficients are reported for reaction of clusters in the range 3–35 metal atoms, at temperatures 279, 300, and 372 K in He buffer gas at 1 and 2 Torr pressure. Rate coefficients generally decrease with increasing temperature, as expected for a mechanism involving formation of a weakly bound precursor complex. By comparison with surface chemistry studies of nitrogen adsorption on molybdenum and tungsten, the reactivity trend with cluster size is interpreted as reflecting the geometric configurations of metal atoms on the surfaces of the clusters. It is suggested that structural transitions occur in molybdenum clusters in the size range 13–20 metal atoms. Evidence is described that suggests that cluster reaction products have nitrogen bound in both atomic and molecular forms. Bulk surfacelike reactivity of the clusters appears to be established in the range 25–30 metal atoms.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 6852-6861 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report cross sections for fluorescence quenching and branching ratios for chemical reaction in collisional deactivation of Ga(5s1 2S1/2) by added gases at room temperature following resonance 4p1 2P(open circle)1/2 →5s1 2S1/2 excitation at 403.30 nm with a pulsed laser. Total quenching cross sections are obtained from Stern–Volmer analysis of fluorescence lifetimes. Chemical contributions to fluorescence quenching are investigated by a pump and probe technique involving saturation of the resonance transition by a pump laser pulse to produce a known fraction of gallium atoms in the excited state, and measurement of the depletion of the gallium atom concentration due to chemical reaction in the excited state. Relative concentration measurements in the presence and absence of the saturating pump pulse are by resonance fluorescence excitation by a probe laser pulse suitably delayed relative to the pump pulse. An analysis of the experiment in terms of rate equations shows how branching ratios for chemical reaction may be obtained from the depletion measurements. Fluorescence quenching cross sections (A(ring)2) are large for N2O (99±10), CO2 (100±20), CH4 (55±6), C2H6 (77±20), C3H8 (100±20), n-C4H10 (130±20), and C2H4 (75±20), moderately large for CO (11±4) and N2 (8±2), and very small for CF4 (〈0.3) and H2 (〈0.05). Among the efficient quenchers only C2H4 showed no detectable contribution from chemical quenching. Branching ratios for chemical removal of Ga(5 2S1/2) are N2O (0.96+0.04−0.1), CO2 (0.55±0.1), CH4 (0.27±0.07), C2H6 (0.33±0.1), C3H8 (0.26±0.1), and C2H4 (0.0+0.05−0.0). Results for H2 and the alkane hydrocarbons are discussed with reference to simple concepts of orbital interactions in the entrance channel.
    Type of Medium: Electronic Resource
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