Noncovalent interactions: a challenge for experiment and theory

It is shown that under the usual conditions of zero‐electron‐kinetic‐energy, pulsed field ionization (ZEKE–PFI) spectroscopy the lifetimes of very high‐lying Rydberg states are increased by at least approximately the factor n (in addition to the expected factor of n3), the principal quantum number, due to strong l mixing by the Stark effect. Additional factors may increase lifetimes by still another factor of approximately n. Pulsed field ionization under typical conditions is shown as likely to be predominantly diabatic and the effect on resolution is assessed. Factors affecting rotational line intensities are also discussed.

Factors affecting lifetimes and resolution of Rydberg states observed in zero-electron-kinetic-energy spectroscopy

The developement of a new mass selective method is reported for the determination of the optical spectra of molecular ions and for the production of state selected ions.(AIP)

Mass analyzed threshold ionization spectroscopy

OH stretching vibrations of phenol-(H2O)n (n=1-3) complexes observed by IR-UV double-resonance spectroscopy

The S1←S0 000 transitions of phenol and the hydrogen bonded phenol(H2O)1 cluster have been studied by high resolution fluorescence excitation spectroscopy. All lines in the monomer spectrum are split by 56±4 MHz due to the internal rotation of the −OH group about the a axis. The barrier for this internal motion is determined in the ground and excited states; V2″=1215 cm−1, and V2′=4710 cm−1. The rotational constants for the monomer in the ground state are in agreement with those reported in microwave studies. The excited state rotational constants were found to be A′=5313.7 MHz, B′=2620.5 MHz, and C′=1756.08 MHz. The region of the redshifted 000 transition of phenol(H2O)1 shows two distinct bands which are 0.85 cm−1 apart. Their splitting arises from a torsional motion which interchanges the two equivalent H atoms in the H2O moiety of the cluster. This assignment was confirmed by spin statistical considerations. Both bands could be fit to rigid rotor Hamiltonians. Due to the interaction between the overal...

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High resolution uv spectroscopy of phenol and the hydrogen bonded phenol/water cluster

The ionization energy of nitric oxide

Three rare gas halide (RgX−) anions, ArBr−, ArI−, and KrI−, and the corresponding open‐shell van der Waals complexes, ArBr, ArI, and KrI, were studied with anion zero electron kinetic energy (ZEKE) spectroscopy. Photodetachment of each anion accesses the three lowest‐lying electronic states (the X1/2, I3/2, and II1/2 states) of the neutral complex. The spectra for each system reveal well‐resolved progressions in the low frequency vibrations of the anion and the three neutral electronic states, providing a detailed spectroscopic probe of the Rg⋅X− and Rg⋅X interaction potentials. The line shapes observed in the ZEKE spectra are analyzed in terms of the line strengths of the underlying rotational transitions. From our data, we construct the potential energy curve for each neutral state as well as for the anion, and these interaction potentials are compared to potentials obtained from scattering and ion mobility experiments.

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Study of the ArBr−, ArI−, and KrI− anions and the corresponding neutral van der Waals complexes by anion zero electron kinetic energy spectroscopy

Two‐photon, two‐color (1+1’) zero‐kinetic‐energy (ZEKE) photoelectron spectra are presented for the 1:1 phenol‐water complex, a prototype system for hydrogen bonding between an aromatic molecule and a simple solvent. ZEKE spectra via different (intermolecular) vibrational intermediate S1 levels of the fully protonated complex (C6H5OH–H2O, h3) as well as the ZEKE spectrum via the vibrationless S1 state of the threefold deuterated complex (C6H5OD–D2O, d3) have been recorded. The spectra are rich in structure, which is mainly attributable to intermolecular vibrations of the ionic complex. Progressions of the intermolecular stretch vibration (240 cm−1) in combination with different intermolecular and intramolecular vibrational levels are the dominant feature of all ZEKE spectra obtained and indicate a large change in the complex geometry along the hydrogen‐bond coordinate on ionization. Comparison between the spectrum of the d3 complex and the spectra via different intermediate intermolecular levels of the h3 complex has allowed a more detailed analysis of the intermolecular features compared to previously reported results. Finally, the vibrational assignments obtained are compared with ab initio results for the phenol‐water cation reported in the following paper in this issue.

Zero-kinetic-energy photoelectron spectroscopy of the hydrogen-bonded phenol-water complex

Rotationally resolved ‘‘zero kinetic energy (ZEKE)’’ electron spectra of ammonia obtained in a 2+1 photon two‐color pump–probe experiment are reported. The rovibronic states with J’=3, K’=1 (ortho‐NH3) and J’=3, K’=2 (para‐NH3) in the B (1E‘) v2=2 state are used as intermediate resonances. Rotational energy levels of the NH+3 ion in two vibrational states of the X+ (2A‘2) electronic ground state, v+2 =1 and 2, are observed in the ZEKE spectra. The rotational constants are: B+=10.19±0.03 cm−1 and C+=5.30±0.04 cm−1 for v+2 =1, and B+ =9.77±0.04 cm−1 and C+ =5.39±0.05 cm−1 for v+2 =2. The adiabatic ionization energies are determined as 83 062.5±1 cm−1 for X+ v2=1 and 84 002.9±1 cm−1 for X+ v2=2, with respect to the lowest (unoccupied) v2=0+, J‘=0, K‘=0, Γevr=A1 rotational state of the X (1A’1) electronic ground state of NH3. The observed propensity rules for the change in K quantum number ion←neutral in the rotational ZEKE transitions are explained from ‘‘near symmetry’’conservation rules in electronica...

Georg Reiser

Papers

The ionization energy of nitric oxide

Study of the ArBr−, ArI−, and KrI− anions and the corresponding neutral van der Waals complexes by anion zero electron kinetic energy spectroscopy

Zero-kinetic-energy photoelectron spectroscopy of the hydrogen-bonded phenol-water complex

High-resolution zero kinetic energy electron spectroscopy of ammonia

A new approach to vibrational spectroscopy of ion clusters: the “zero kinetic energy (ZEKE)” photoelectron spectrum of the phenol—water complex