Molecular Structure
Jump to navigation
Jump to search
Molecular structure (molecular geometry) is a one of the most fundamental properties of molecules, which characterizes spatial positions of the atoms that constitute a molecule. This term is usually referred to the geometrical structure of molecules in gas phase.
Types of molecular structure
Abbreviations are:
- QC — Quantum-chemical calculations
- GED — Gas electron diffraction
- MW — Microwave spectroscopy
- HRMS — High resolution molecular spectroscopy
Type | Description | Methods |
---|---|---|
re | Equilibrium structure. Appears as a result of Born-Oppenheimer approximation in quantum mechanics. | QC |
rg | Thermally averaged structure.[gt 1] rg distances are centers of gravity for corresponding distribution functions P(r). | GED |
ra | Average structure [gt 1] used for calculation of molecular scattering intensity in GED theory. | GED |
rα = rh0 | Distances between average nuclear positions.[gt 2] | GED, MW, HRMS |
r0α, rz | Distances between average nuclear positions at 0 K, i.e. for ground vibrational state.[gt 2] | GED, MW, HRMS |
rh1 | Distances between average nuclear positions calculated taking into account nonlinear relationships between internal and Cartesian coordinates.[gt 2] | GED, MW, HRMS |
ra3,1 | Semi-experimental equilibrium structure obtained using corrections calculated by Shrink program utilizing cubic force fields. | GED, MW, HRMS |
rsee | Semi-experimental equilibrium structure obtained using a set of theoretically calculated corrections to experimental and/or operational data. | GED, MW, HRMS |
rs | Effective structure derived from isotopic differences in rotational constants. | MW, HRMS |
r0 | Effective structure derived from rotational constants of zero-point vibrational level. | MW, HRMS |
rm | Effective structure derived from the mass-dependence method of Watson. | MW, HRMS |
rρm | Effective structure similar to rm obtained by a slightly modified method of Harmony et al. | MW, HRMS |
- ↑ 1.0 1.1 Interatomic distances are averaged over molecular vibrations for a given temperature. Generally such distances are geometrically inconsistent.
- ↑ 2.0 2.1 2.2 In contrast to rg, where subject to averaging are interatomic distances, here atomic positions are averaged. Therefore this structure is geometrically consistent.