Theoretical and (e,2e) Experimental Investigation into the Complete Valence Electronic Structure of [1.1.1]Propellane

W Adcock,M T Michalewicz,M J Brunger,D A Winkler,W Von Niessen,I E Mccarthy,C I Clark,E Weigold

doi:10.1021/ja963058f

W Adcock, M T Michalewicz + Show 6 more

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https://doi.org/10.1021/ja963058f

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Abstract

An electronic structural study of the complete valence shell of [1.1.1]propellane is reported. Binding energy spectra were measured in the energy regime of 3.5−46.5 eV over a range of different target electron momenta, so that momentum distributions (MDs) could be determined for each ion state. Each experimental electron momentum distribution is compared with those calculated in the plane wave impulse approximation using both a triple-ζ plus polarization level SCF wave function and a further 13 basis sets as calculated using density functional theory. A critical comparison between the experimental and theoretical momentum distributions allows us to determine the optimum wave function for [1.1.1]propellane from the basis sets we studied. In general, the level of agreement between the experimental and theoretical MDs for this optimum wave function for all of the respective valence orbitals is fair. The determination of this wave function then allows us to derive the chemically interesting molecular properties of [1.1.1]propellane. A summary of these results and a comparison of them with those of other workers are presented with the level of agreement typically being good. In particular, we note that we confirm the existence of the C1−C3 bridging bond with a bond order of 0.70.

Highlights

IntroductionElectron momentum spectroscopy (EMS), or (e,2e) coincidence spectroscopy, is a well-developed tool for the investigation of the dynamic structure of molecules due to its unique ability to measure the orbital momentum profile for binding-energy-selected electrons. within the plane wave impulse approximation (PWIA) and, in many cases, the target Hartree-Fock (THFA) approximation, this measured momentum cross section may be directly compared with the calculated spherically averaged momentum distribution (MD) of a specific molecular orbital, once the appropriate angular-resolution function has been folded in. EMS is a powerful technique for evaluating the quality of theoretical wave functions in quantum chemistry, and in this paper we report its application to the saturated hydrocarbon [1.1.1]propellane (C5H6)
Each experimental electron momentum distribution is compared with those calculated in the plane wave impulse approximation using both a triple- plus polarization level SCF wave function and a further 13 basis sets as calculated using density functional theory
The significance of the present application of the Electron momentum spectroscopy (EMS) technique to this molecule is that by comparing the experimental and theoretical momentum distributions (MDs), for the relevant valence orbitals, we can independently determine which of the SCF or density functional theory (DFT) basis sets of states we have studied provides the most physically reasonable representation of the [1.1.1]propellane molecule

Summary

Introduction

Electron momentum spectroscopy (EMS), or (e,2e) coincidence spectroscopy, is a well-developed tool for the investigation of the dynamic structure of molecules due to its unique ability to measure the orbital momentum profile for binding-energy-selected electrons. within the plane wave impulse approximation (PWIA) and, in many cases, the target Hartree-Fock (THFA) approximation, this measured momentum cross section may be directly compared with the calculated spherically averaged momentum distribution (MD) of a specific molecular orbital, once the appropriate angular-resolution function has been folded in. EMS is a powerful technique for evaluating the quality of theoretical wave functions in quantum chemistry, and in this paper we report its application to the saturated hydrocarbon [1.1.1]propellane (C5H6). The analysis of the total electron density obtained from ab initio calculations by Wiberg and co-workers showed these descriptions to be misleading Their results indicated three major conclusions including that there is a qualitative difference between the electron density in the bridging region of [1.1.1]propellane and of the analogous bicyclic species, bicyclo[1.1.1]pentane. Standard UniChem features allow us to utilize this optimum wave function to extract the chemically important molecular property information for the [1.1.1]propellane system including bond lengths, bond orders, electron density (3D), and electron density contour (2D) plots and its infrared spectra These data and a comparison with previous work are given and discussed in section 5 of this paper.

Experimental Details

Theoretical Analysis

Comparison between Experimental and Theoretical Momentum Distributions

Findings

Conclusions