Probability Density Analysis Reveals Substantial Differences Between the Dinitrogen and Acetylene Triple Bonds

In earlier publications, it was shown that the electron positions maximizing the probability density <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow> <mml:msup><mml:mfenced><mml:mi>Ψ</mml:mi></mml:mfenced> <mml:mn>2</mml:mn></mml:msup> </mml:mrow> <mml:annotation>$$ {\left|\Psi \right|}^2 $$</mml:annotation></mml:semantics> </mml:math> resemble the Lewis structures for most small molecules. While this holds for the triple bond in acetylene, this is not the case for the triple bond in dinitrogen. Because of recent advances in studying the topology of wave functions, this peculiar case is revisited. In this work, the dinitrogen wave function is analyzed and compared to that of acetylene. Significant differences of the electron positions maximizing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow> <mml:msup><mml:mfenced><mml:mi>Ψ</mml:mi></mml:mfenced> <mml:mn>2</mml:mn></mml:msup> </mml:mrow> <mml:annotation>$$ {\left|\Psi \right|}^2 $$</mml:annotation></mml:semantics> </mml:math> are uncovered and explained by the presence of hydrogen atoms in acetylene and by electron arrangements resulting from calculations of the nitrogen and carbon atoms. Moreover, insights into the electron delocalization of both molecules are gained by investigating electron exchange paths. Considering the different chemical behaviors of dinitrogen and acetylene, these differences should be expected.