Mehrdimensionale Bewegungen mit großer Amplitude: Aufdeckung simultaner Tunnelpfade in Molekülen mit mehreren internen Rotoren

Abstract

Licht in das Dunkel: Die ausführbaren Tunnelpfade eines Moleküls geben Aufschluss über die Wechselwirkungsmechanismen, die seine interne Dynamik steuern. In der Reihe (CH3)3XCl (X=Si, Ge, Sn) nimmt die elektrostatische Abstoßung zwischen den Methylgruppen ab, während die chemische Bindung an Bedeutung gewinnt. Eine Kombination aus Rotationsspektroskopie, Permutations‐Inversions‐Gruppentheorie und mehrdimensionalem Tunnelformalismus gibt Einblick in das dynamische Verhalten.

Kinetic Study of Methyl Isobutyl Ketone Combustion over a Commercial Pt/Alumina Catalyst

“…As mentioned, such a lifting of accidental degeneracies has not been observed for (CH 3 ) 3 SiCl41 and (CH 3 ) 3 GeCl 42. One might wonder if a significantly larger nuclear quadrupole moment coupling constant in the presence of large‐amplitude motions can also lift spectral degeneracies of some hyperfine patterns as observed in (CH 3 ) 3 SnCl, for which the nuclear quadrupole coupling is small but the torsional barrier is lower and thus very dominant torsional coupling is present 39. 40 Bromine, for example, has an about eight times larger nuclear quadrupole moment coupling constant than that for chlorine (+33.1(4) Q fm −2 for 79 Br and −8.11(8) Q fm −2 for 35 Cl21).…”

“…As mentioned, both steric repulsion and the characters of the chemical bonds are responsible for the barrier height to internal rotation, and their relative contributions in various molecular situations are in general different. Here, we report on the investigation of the series (CH 3 ) 3 XCl (X=Si, Ge, Sn),39 the central atoms of which are of increasing size (the covalent radii of the central atoms in this series change significantly from 1.17 and 1.22 Å for Si and Ge, respectively, to 1.40 Å for Sn), so that electrostatic repulsion and thus top–top communication through space is gradually reduced from Si via Ge to Sn. Consequently, the relative contributions of the character of the chemical bond XCH 3 (X=Si, Ge, Sn) become more important, thus leading to the dramatic differences observed for the molecular internal dynamics.…”

Understanding High‐Resolution Spectra of Nonrigid Molecules Using Group Theory

“…(Note that the definitions of the matrix elements H L and H E here and in the Supporting Information for ref. [39] are exchanged with respect to those used in refs. [40,42].…”

“…Here, we report on the investigation of the series (CH 3 ) 3 XCl (X = Si, Ge, Sn), [39] the central atoms of which are of increasing size (the covalent radii of the central atoms in this series change significantly from 1.17 and 1.22 for Si and Ge, respectively, to 1.40 for Sn), so that electrostatic repulsion and thus top-top communication through space is gradually reduced from Si via Ge to Sn. Consequently, the relative contributions of the character of the chemical bond XÀCH 3 (X = Si, Ge, Sn) become more important, thus leading to the dramatic differences observed for the molecular internal dynamics.…”

“…[42] One might wonder if a significantly larger nuclear quadrupole moment coupling constant in the presence of large-amplitude motions can also lift spectral degeneracies of some hyperfine patterns as observed in (CH 3 ) 3 SnCl, for which the nuclear quadrupole coupling is small but the torsional barrier is lower and thus very dominant torsional coupling is present. [39,40] Bromine, for example, has an about eight times larger nuclear quadrupole moment coupling constant than that for chlorine (+33.1(4) Q fm À2 for 79 Br and À8.11(8) Q fm À2 for 35 Cl [21] ). Both nuclei have a quadrupole spin of 3/2.…”