Rotationally resolved photoelectron angular distributions in resonance enhanced multiphoton ionization of NO

We report calculated ionic rotational branching ratios and associated photoelectron angular distributions for (1+1′) resonance enhanced multiphoton ionization (REMPI) via the R_(21)(20.5), P_(21)+Q_(11)(25.5), and P_(11)(22.5) branches of the A ^2 Σ^+(3sσ) state of NO. The branching ratios are dominated by even angular momentum transfer peaks, in agreement with the ΔN+l=odd (ΔN≡N+−Ni ) selection rule. Whereas the calculated photoelectron angular distributions are very branch dependent alignment, the ionic branching ratios are found to be less so. The present calculated results agree well with the experimental results of Allendorf et al

Cooper minima and rotationally resolved resonance enhanced multiphoton ionization spectroscopy

We demonstrate that a Cooper minimum, close to threshold, in photoionization via an excited molecular Rydberg state can have a dramatic influence on the ionic rotational branching ratios. It is also shown that this behavior can be exploited to produce ions selectively in a specific rotational level. To illustrate this effect we present the results of ab initio calculations for (2+1′) resonance enhanced multiphoton ionization via the O_(11) (23.5) branch of the H ^2Σ^+(3d,4s) state of NO, where a Cooper minimum is found in l=3 of the kσ and kπ continua at photoelectron kinetic energies of 2.6 eV and 2.9 eV, respectively

Nonempirical Calculations on Excited States: The Ethylene Molecule

A series of nonempirical calculations are reported on the excited states of the ethylene molecule using a recent minimum basis set LCAO MO SCF wavefunction. For the lowest excited singlet state of ethylene (^1B_(3u)) the coupling between the π electrons and σ electrons is significant: the excitation energy being decreased from 11.98 to 10.17 eV and the oscillator strength from 1.03 to 0.73. This coupling has little effect on the triplet state. In the next higher approximation (the random‐phase approximation) the excitation energy is further decreased to 9.44 eV and the transition moment to 0.51. With the use of accurate LCAO MO SCF wavefunctions, it is felt that the methods presented here will provide a basis for the theoretical interpretation of electronic spectra

Rotational branching ratios at low photoelectron energies in resonant enhanced multiphoton ionization of NO

We report calculated rotational branching ratios for very low energy (50 meV) photoelectrons resulting from (1+1′) resonant enhanced multiphoton ionization (REMPI) via the J_i =1/2, 3/2, 5/2, and 7/2 levels of the P_(11) branch of the A ^2Σ^+ (3sσ) state of NO. Even angular momentum transfer (ΔN≡N_+−N_i) peaks are dominant in these rotational distributions, in agreement with the selection rule ΔN+l=odd. Angular momentum coupling in the photoelectron wave function arising from the molecular ion potential leads to smaller but appreciable ΔN=odd peaks. The calculated ΔN=0 to ΔN=+2 peak ratios show the same strong decrease when J_i increases from 1/2 to 3/2 as seen in the experimental zero‐kinetic‐energy (ZEKE) photoelectron spectra [Sander et al., Phys. Rev. A 36, 4543 (1987)], but do not show the rapid die‐off of the ΔN≠0 peaks for higher J_i observed experimentally. The calculated trend in the ΔN=+2 vs ΔN=0 peaks could be understood on the basis of simple angular momentum transfer arguments. These same arguments indicate that this trend in the ΔN=0 and +2 peaks with increasing angular momentum is not generally expected in other branches. Spectra via the R_(21) ( J) branch are presented to support this assertion. We also present photoelectron angular distributions which show a strong dependence on ΔN reflecting the changing composition of the photoelectron wave function

Low-energy electron scattering from C_4H_9OH isomers

We present differential, integral, and momentum-transfer cross sections for elastic scattering of low-energy electrons by three butanol isomers, isobutanol, t-butanol, and 2-butanol. Our results were calculated with the Schwinger multichannel method in the static-exchange plus polarization approximation for collision energies from 1 to 50 eV. The present results are compared with previous calculations and measurements for the remaining C_4H_9OH isomer, n-butanol [Khakoo et al., Phys. Rev. A 78, 062714 (2008)]. Distinctive behavior is observed in the differential cross sections at collision energies between 5 and 10 eV. In particular, whereas n-butanol exhibits an f-wave scattering pattern, the other isomers exhibit d-wave behavior. A similar pattern is found in the related alkanes when comparing straight-chain versus branched isomers. We discuss the possible connection of this behavior to shape resonances that influence the scattering

Low-energy electron scattering by C_2HF_5

We report elastic and electronically inelastic cross sections for low-energy electron scattering by pentafluoroethane, C_2HF_5. Our calculations were performed using the Schwinger multichannel method. For elastic scattering, we calculated integral, differential, and momentum transfer cross sections for energies from 5 to 50 eV. In the inelastic case, we obtained integral and differential cross sections for electron-impact excitation of the 1 1,3A[prime] and 2 1,3A[prime] excited states at the three-channel level of approximation. At higher energies, the elastic differential cross sections are quite similar to existing theoretical results for C_2F_6. Limited electronic-structure calculations were carried out to explore the dissociation behavior of the excited states

Low-energy electron scattering by N2O

We present elastic integral, differential, and momentum-transfer cross sections for electron collisions with N2O. We show that, with a slight modification of a method of incorporating polarization effects proposed recently by us [Winstead, McKoy, and Bettega, Phys. Rev. A 72, 042721 (2005)] along with a flexible one-particle basis set, we can reproduce features in the experimental data that were not reproduced by earlier calculations. We also find evidence of a Ramsauer-Townsend minimum, which our calculation places at about 0.2 eV

Elastic scattering of low-energy electrons by benzene

We present elastic cross sections obtained from ab initio calculations for low-energy electron scattering by benzene, C6H6. The calculations employed the Schwinger multichannel method as implemented for parallel computers within both the static-exchange and static-exchange-polarization approximations. We compare our results with other theoretical calculations and with available experimental data. In general, agreement is good

Opportunity-Rich Schools and Sustainable Communities: Seven Steps to Align High-Quality Education With Innovations in City and Metropolitan Planning and Development

Details challenges and steps for linking quality education and community and economic vitality, including establishing a shared vision and metrics, aligning investments for prosperity, and expanding access via transportation. Lists promising practices