Resonant two-photon ionization-photoelectron spectroscopy of Cu2: Autoionization dynamics and Cu+2 vibronic states

Abstract

Resonant two-photon ionization of gas phase CU 2 in a cold molecular beam in conjunction with time-of-flight photoelectron spectroscopy provides new vibronic state spectroscopic infonnation for the dimer cation Cu 2 + . One color ionization via the 0-0, 1-0, and 2a-O bands of Smalley's System V neutral CU2 resonant states (J ..... X transition) accesses Cut states in the range 0-1.4 eV. The electron kinetic energy measurements slightly refine the first adiabatic ionization energy ofCu 2 to II (Cu 2 ) = 7.899 ± 0.007 eV. We observe two electronic states of CU2+ which we assign as X 2~t and an excited 2n spin-orbit pair of sublevels with origins at TOen3/2) = 1.143 ± 0.002 eVand T O en 1 /2) = 1.256 ± 0.002 eV. The absence of spin -orbit splitting identifies the ground state 2~ symmetry; the spin-orbit splitting of 898 ± 8 cm-1 identifies the excited states as 2n. Within X 2~g+ we observe a remarkably long vibrational progression, perhaps extending from v = 0-80. The vibrational intervals detennine the constants We = 188 ± 4 cm-I and w.xe = 0.75 ± 0.09 cm-I . The 2n vibrational intervals detennine We = 244 ± 6 cm -I. The adiabatic bond dissociation energy of ground state Cut is Do(Cu+ -Cu) = 1.84 ± 0.08 eV. The intensity pattern oftheX2~g+ vibrational bands exhibits multiple peaks whose positions and amplitudes are sensitive to the resonant J state vibrational level. For 0-0 excitation, we observe reproducible band intensity alternation. We present preliminary mass spectral and photoelectron data indicating that the cause of the highly non-Franck-Condon band intensities is excitation oflong lived, dissociative autoionization states which undergo extensive nuclear motion on the time scale of electron ejection. We propose an autoionization mechanism that includes a description of the CU 2 J state and explains the observed phenomena invoking only one electron transition.3854 Sappey. Harrington. and Weisshaar: Spectroscopy of CU 2 Pi = (J-lJ26/J-li) 1/2, where J-l126 = 31.46 amu is the reduced

Imaging the photodissociation dynamics of neutral metal clusters: copper dimer, Cu2, and copper oxide, CuO

“…In the majority of studies reported here, this UV probe pulse was fixed to be resonant at the one-photon level with the J (v = 0) ' X (v = 0) transition in 63 Cu 2 (previously Smalley's ''system V'') 11 at 267.06 nm. 1,21 In two-colour experiments, especially in the study of CuO, a second pump pulse, comprising the signal output of a 355 nm pumped optical parametric oscillator (Continuum Panther) is arranged to co-propagate with the UV beam and fires typically 30 ns before the probe. This delay is sufficient to permit resolution of visible only and true twocolour processes in the time-of-flight spectrum which proved useful in simplifying the analysis.…”

“…This process has been studied in detail by Sappey et al using photoelectron spectroscopy (PES). 20,21 The Cu 2 + spectrum is mirrored approximately in the Cu + channel indicating a significant degree of photofragmentation. By way of investigating the likely fragmentation mechanism(s) involved we have recorded one-colour VMI images at this wavelength and the resulting total kinetic energy release (TKER) spectrum is shown in the lower portion of the Fig.…”

“…[6][7][8][9] Small isolated copper clusters, including the dimer, were first studied spectroscopically in the early 1980s by the Smalley group [10][11][12][13] and others. 14 Since then the isolated dimer alone has been studied by techniques such as fluorescence, [14][15][16] direct absorption, 17 FT emission, 18 photoionization spectroscopy, [19][20][21] and collision induced dissociation (CID) techniques. 22,23 Computationally, Miyoshi et al performed a series of high quality ab initio calculations on Cu 2 24 and developments since have been reviewed recently by Lecoultre et al in their time-dependent density functional theory study.…”

Observation of a gerade symmetry state of Cu2 using two‐color resonant four‐wave mixing

“…u state by the rotational P(10) transition from the electronic ground state, (b) is obtained by exciting the band origin v ′ = 0 by P (10), and (c) shows the energy diagram and transitions involved for the UNFOLDED two-color resonant four-wave mixing scheme. Δ indicates the energy interval between levels of B0 + u v ′ = 1 J ′ = 9 and B0 + u v ′ = 0 J ′ = 9 0 + g state from v ′ = 0 by the UNFOLDED double-resonance scheme, the P(9) and R(9) transitions are expected to occur in a wavenumber region shifted by +241.81 cm −1 , which is the energy difference of the v ′ = 1 and v ′ = 0 levels in the B0 + u state.…”

“…By opening the d-shell upon excitation of an electron, a complex electronic configuration is obtained that is typical for transition metals thus providing an unique opportunity to understand the role of the d-orbitals in chemical bonding. [1,2] As such, extensive experimental [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] and theoretical work [19][20][21][22][23][24] have focused on the ground and excited electronic levels of Cu 2 . The electronic ground state has been identified as X 1 Σ + g state in Hund case (a) notation.…”