Measurements of mass-selected ion-current and threshold photoelectron spectra of jet-cooled aniline–Arn van der Waals complexes (n=1 and 2) have been carried out with a two-color resonantly enhanced multiphoton ionization (REMPI) technique using a high-resolution threshold photoelectron analyzer developed in this laboratory. From our (1+1′) REMPI experiments via the respective excited S1 states, we have obtained photoelectron spectra with well-resolved vibrational progressions due to ‘‘low-frequency van der Waals modes’’ of the cations; νvdW=16 cm−1 (n=1) and νvdW=11 cm−1 (n=2). From Franck–Condon calculations, we have assigned these low-frequency vibrations to the ‘‘van der Waals bending’’ of the cations. We have also found that the angles of the van der Waals bonds in the cations are changed by 8.2 (n=1) and 8.8 (n=2) degrees with respect to the S1 states. The adiabatic ionization potentials (Ia) of aniline and the aniline–Arn complexes (n=1 and 2) have been determined as 62 268±4 cm−1 (aniline), 62 157±4 cm−1 (n=1), and 62 049±4 cm−1 (n=2). Their shifts ΔIa are 111 cm−1 (n=1) and 219 cm−1 (n=2) with respect to aniline. Spectral shifts due to complex formation have been observed for a total of 13 ring modes of the cations.

We report an electron momentum spectroscopy study of vibrational effects on the electron momentum distributions for the outer valence orbitals of ethylene (C(2)H(4)). The symmetric noncoplanar (e,2e) experiment has been conducted at an impact energy of 1.2 keV. Furthermore, a theoretical method of calculating electron momentum distributions for polyatomic molecules has been developed with vibrational effects being involved. It is shown from comparisons between experiment and theory that taking into account effects of the CH(2) asymmetric stretching and CH(2) rocking vibrational modes of C(2)H(4) is essential for a proper understanding of the electron momentum distribution of the 1b(3g) molecular orbital.

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A new apparatus has been developed to detect and measure angular correlations between energy-selected photoelectrons and coincident mass-analyzed fragment ions from photoionization at selected wavelengths. It achieves velocity imaging for electrons and ions simultaneously and has high collection efficiency for both particles, with moderate mass and energy resolution. Angular and energy correlations between the two particles are measured, as are the angular distributions of each particle independently relative to the light polarization direction. Fixed-molecule electron angular distributions are deduced in cases of pure axial recoil. Examples of angular distributions from photoionization of diatomic molecules are reported.

Articles you may be interested inTwo-dimensional laser induced fluorescence spectroscopy of van der Waals complexes: Fluorobenzene-Ar n (n = 1,2) J. Chem. Phys. 136, 134309 (2012); 10.1063/1.3697474 X-ray photoelectron spectroscopy study of polyimide thin films with Ar cluster ion depth profiling J. Vac. Sci. Technol. A 28, L1 (2010); 10.1116/1.3336242Low lying electronic states of rare gas-oxide anions: Photoelectron spectroscopy of complexes of O − with Ar, Kr, Xe, and N 2 Fragmentation energetics and dynamics of fluorobenzeneAr n (n=1-3) clusters studied by mass analyzed threshold ionization spectroscopy In this work, the molecules styrene (ST) and phenylacetylene (PA), as well as their argon complexes ST -Ar and PA-Ar, have been investigated with (1 + 1') resonance enhanced multiphoton ionization (REMPI) threshold photoelectron spectroscopy (TES). The first adiabatic ionization energies of ST, PA, ST -Ar, and PA-Ar have been measured as 68 267 ± 5, 71175±5, 68 151 ±5, and 71 027±5 cm-I , respectively. For both ST-Ar and PA-Ar, the first photoelectron band shows structure in the lowest frequency van der Waals (vdW) bending mode in the ground ionic state, with VydW being measured as 15 cm-I in each case. For each molecule excitation to a particular vibrational level of the S I state followed by ionization, allows structure in that mode to be observed in the threshold photoelectron spectrum. This has been achieved for three modes in both styrene and phenylacetylene. The experimental ionic vibrational frequencies thus obtained, have been compared with those known for the So and S I states.a)IMS Visiting Fellow. Permanent address:

Over the last four decades an experimental method has been developed for looking at electron orbitals in momentum space. The method, called electron momentum spectroscopy (EMS), is based on the electron-impact ionizing reaction near the Bethe ridge at incident electron energies of the order of 1 keV or higher. This account reviews frontiers of the field, involving the first approach to molecular frame EMS that enables one to look at molecular orbitals in three-dimensional form.

Measurements and calculations of the contribution of the non-dipole terms in the angular distribution of photoelectrons from the K-shell of randomly oriented N2 molecules are reported. The angular distributions have been measured in the plane containing the photon polarization and the photon momentum vectors of linearly polarized radiation. Calculations have been performed in the relaxed core Hartree–Fock approximation with a fractional charge, and many-electron correlations were taken into account in the random phase approximation. Both theory and experiment show that the non-dipole effects are rather small in the photon energy region from the ionization threshold of the K-shell up to about 70 eV above it. From the theory, it follows that the non-dipole terms for the individual 1σg and 1σu shells are considerably large; therefore measurements resolving the contributions of the 1σg and 1σu shells are desirable.

Angular distributions of C 1s photoelectrons from fixed-in-space CO molecules have been measured with vibrational resolution. A strong dependence of the angular distributions on the vibrational states of the residual molecular ion has been found for the first time in the region of the shape resonance. Calculations in the relaxed core Hartree-Fock approximation have reproduced the angular distributions fairly well in the general shapes of the angular distributions due to the correct description of nuclear motion as an average of the internuclear-distance-dependent dipole amplitudes.