Comprehensive Experimental and Theoretical Study into the Complete Valence Electronic Structure of Norbornadiene

Abstract

Momentum Distributions (MDs), obtained using high-resolution electron momentum spectroscopy (HREMS), are reported for norbornadiene's 18 valence orbitals. Corresponding theoretical results, using generalized gradient approximation density functional theory (DFT) together with TZVP, DZVP, and DZVP2 basis functions and a plane wave impulse approximation to describe the ionization process, are also detailed. This work represents the first comprehensive HREMS/DFT investigation into the complete valence electronic structure of norbornadiene (NBD), with significant results being obtained. In particular, an exacting comparison between our experimental and theoretical MDs enables us to define the “optimum” basis for NBD, from those we studied. This “optimum” basis is then used to extract a wide range of NBD's important molecular property information, which are subsequently compared with the results of independent measurements and calculations. Agreement between our results and those from independent measurements was generally very good, highlighting the utility of HREMS in a priori basis set evaluation.

Norbornane: An investigation into its valence electronic structure using electron momentum spectroscopy, and density functional and Green’s function theories

“…Specifically, in this region all the PWIA-BLYP/ DFT MD's exhibit a somewhat higher cross section magnitude compared to all the corresponding PWIA-BP/DFT MD's with the experimental cross sections favoring the PWIA-BP/DFT results. This is quite unusual in our experience 10,15,16 as typically we have found that our experimental MD's are more discriminating in terms of the types of basis sets employed, rather than the type of XC functional used. We would characterize the overall level of agreement between our PWIA-BP/DFT momentum distribution results and the experimental momentum distributions as being good, suggesting EMS spectroscopic factors for each of these orbitals lying somewhere in the range 0.9-1.0.…”

“…Finally, we note that norbornane is the second molecule in the chemically similar series norbornadiene͑I͒, 15,16 norbornene͑II͒, and norbornane͑III͒, which we have studied using EMS, HF, and DFT techniques. In going from I to III the CϭC double bonds in these highly strained bicyclic hydrocarbons are progressively saturated.…”

Structural impact on the methano bridge in norbornadiene, norbornene and norbornane

“…Our EMS results for NBD have been discussed in detail previously [8,9]. Here, we simply reproduce and discuss our experimental and theoretical orbital momentum densities for the 3b 2 orbital of norbornadiene.…”

“…Norbornadiene (NBD), on the other hand, is an unconjugated, strained and non-planar diene. It is a prototype for through space and through bond interaction studies, with our recent electron momentum spectroscopy (EMS) study confirming the through space interaction dominance in NBD [8,9].…”

“…It would therefore be nice to have an a priori indication of which of these QM models might provide a reliable representation of the molecules in question. The unique orbital imaging capability of EMS [8,9] provides us with a mechanism for achieving precisely this. In this technique EMS measures orbital momentum densities (MDs) for the molecular orbitals of the species in question, and these are then compared in detail to those correspondingly calculated using the available basis states (from e.g.…”