ALBERT

Notes: The pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectrum of Kr2 has been recorded between 103 500 cm−1 and 118 000 cm−1. Photoelectronic transitions to four [the I(1/2u), I(3/2u), II(1/2u), and II(1/2g) states] of the first six electronic states of Kr2+ have been observed. The photoelectronic transition to the ground I(1/2u) state consists of a long progression of vibrational bands, starting at v+=0. From the resolved isotopic substructure of vibrational levels with v+≥15, the absolute numbering of the vibrational quantum number could be determined. The analysis of the spectrum has led to improved values of the adiabatic ionization potential [IP(I(1/2u))=(103 773.6±2.0) cm−1], the dissociation energy [D0+(I(1/2u))=(9267.8±2.8) cm−1] and to the determination of an analytical potential energy curve that reproduces the experimental data from v+=0 to beyond 81% of the dissociation energy. The transitions to vibrational levels of the I(1/2u) state with v+≤30 and v+≥65 have vanishing Franck–Condon factors for direct ionization from the ground neutral state and gain intensity from transitions to low Rydberg states that belong to series converging on excited electronic states of Kr2+. In the region immediately below the first dissociation limit of Kr2+, a second progression was observed and assigned to a photoelectronic transition to the I(3/2u) state. The adiabatic ionization potential [IP(I(3/2u))=(112 672.4±2.0) cm−1], the dissociation energy [D0+(I(3/2u))=(369.1±2.8) cm−1] and vibrational constants could be extracted for this state. Two further progressions were observed below the second dissociation limit of Kr2+ and assigned to transitions to the II(1/2u) and II(1/2g) states. The adiabatic ionization potentials [IP(II(1/2u))=(117 339.7±2.0) cm−1, IP(II(1/2g))=(117 802.6±2.0) cm−1] and the dissociation energies [D0+(II(1/2u))=(1071.7±2.8) cm−1, D0+(II(1/2g))=(608.8±2.8) cm−1] were determined for these two ionic states. In the region just below the ionic dissociation limits, artifact lines are observed in the PFI-ZEKE photoelectron spectra at the position of transitions to Rydberg states of the krypton monomer. At the lowest threshold, collisional and associative ionization of the long lived atomic Rydberg states leads to the formation of ZEKE electrons; at the upper threshold, the rapid autoionization of the atomic Rydberg states forms high ion concentrations, and the electrons that remain trapped in the ion cloud are released by the delayed pulsed field used to produce and extract the PFI-ZEKE electrons. © 2001 American Institute of Physics.

Notes: The pulsed-field-ionization (PFI) zero-kinetic-energy (ZEKE) photoelectron spectra of CH4 and CD4 have been recorded in the region 100880–104100 cm−1. From the analysis of the photoelectron spectra the first adiabatic ionization potential of CH4 and CD4 has been determined to be (101773±35) cm−1 and (102210±25) cm−1, respectively. A one-dimensional model for the pseudorotation between three equivalent C2v equilibrium structures shows evidence for a fluxional behavior of CH4+. © 1999 American Institute of Physics.

Notes: The pulsed-field-ionization (PFI) zero-kinetic-energy (ZEKE) photoelectron spectrum of Ar2 has been recorded between 116 500 cm−1 and 128 200 cm−1. The spectrum consists of a long progression of transitions to the vibrational levels of the ground A 2Σ1/2u+ state of Ar2+ with v+ up to 52, a shorter progression of four bands attributed to transitions to the first four vibrational levels of the C 2Π1/2u state and of a single sharp line assigned to the C 2Π3/2u(v+=0)←X 10g+(v=0) transition. Rotational constants of several vibrational levels of the A 2Σ1/2u+ state have been determined from high resolution PFI-ZEKE photoelectron spectra. From these measurements new information on the first electronic states of Ar2+ has been extracted. An analytical potential energy function has been derived for the A 2Σ1/2u+ state which extends to large internuclear distances (beyond 5 Å) and reproduces all measured vibrational energy levels up to v+=52. The adiabatic ionization potential for the photoelectronic transitions to the A 2Σ1/2u+, C 2Π3/2u and C 2Π1/2u states are determined to be 116 591.1±6 cm−1, 126 883.9±3 cm−1 and 128 004.1±5 cm−1, respectively, from which dissociation energies (D0+) of 10 603.7±6 cm−1, 310.8±3 cm−1, and 622.5±5 cm−1 are obtained. The vibrational levels of the C 2Π1/2u state can be described by a Morse potential with ωe=58.9±0.8 cm−1 and ωexe=1.40±0.27 cm−1, respectively. Associative ionization and collisional ionization processes involving argon atom Rydberg states induce spurious peaks in the PFI-ZEKE photoelectron spectrum. Ways to unambiguously identify these spurious peaks are discussed. © 1998 American Institute of Physics.

Notes: The high resolution zero-kinetic-energy (ZEKE) photoelectron spectrum of Ar2 has been recorded between 116500 and 128500 cm−1. The spectrum consists of a progression of 52 vibrational bands in the A 2Σ1/2u+←X 1Σg+ (X 10g+ in Hund's case (c) notation) photoelectronic transition. The absolute numbering of the vibrational progression in the A←X transition is achieved by measuring the isotope shifts of two vibrational bands of the 36Ar2 molecule. From the analysis of the vibrational progression the first adiabatic ionization potential of Ar2 has been determined to be 116593.5±6.0 cm−1 (14.4558±0.0007 eV) from which a dissociation energy D0 of 10601.2±6.0 cm−1 (1.3144±0.0007 eV) results for the A 2Σ1/2u+ ground state of Ar2+. The potential curve of the ground ionic state in the vicinity of the potential minimum is adequately represented by a Morse potential with ωe+=307.0±0.4 cm−1 and ωexe+=2.05±0.05 cm−1. The position of higher members of the vibrational progression with v+〉25 cannot be fitted accurately with a Morse potential. © 1997 American Institute of Physics.

Notes: High-resolution zero-kinetic-energy photoelectron spectroscopy has been used to record the transition between the lowest bound state (3s 2A1) of the perdeuterated ammonium radical (ND4) and the X˜ 1A1 ground vibronic state of the perdeuterated ammonium ion (ND4+). The spectra obtained are the first rotationally resolved photoelectron spectra ever measured for a tetrahedral molecule. The analysis of the rotational structure is accompanied by a description of the observed symmetry selection rules and propensity rules for core rotational angular momentum changes that characterize the photoionization process. Rotational constants (B0=2.8560±0.0037 cm−1 and B0+=2.9855±0.0037 cm−1) and centrifugal distortion constants (D0=(4.78±1.4)×10−5 cm−1 and D0+=(4.77±1.5)×10−5 cm−1) have been determined for the 3s 2A1 state of ND4 and the X˜ 1A1 state of ND4+, respectively. The ionic rotational constant is in good agreement with the value B0+=2.9787±0.0029 cm−1 determined indirectly by Crofton and Oka (J. Chem. Phys. 86, 5983 (1987)) from the measurement of allowed transitions of the ν3 vibrational band of ND4+. The neutral rotational constant differs markedly from the ab initio value B0=3.0407 cm−1 of Havriliak and King (J. Am. Chem. Soc. 105, 4 (1983)) used by Alberti, Huber and Watson (J. Mol. Spectrosc. 107, 133 (1984)) as input data to fit the rotational structure of the Schüler band of ND4. The adiabatic ionization potential of ND4 is determined to be 37490.7±1.5 cm−1 (4.64826±0.00019 eV). The large changes in core rotational angular momentum that accompany the removal of the photoelectron may be caused by the Cooper minimum in the s→p photoexcitation/photoionization channel recently predicted by Smith and Chupka [Chem. Phys. Lett. 250, 589 (1996)] to lie in the vicinity of the ionization threshold. © 1997 American Institute of Physics.