Molecular Structure: Difference between revisions
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== Types of molecular structure == | == Types of molecular structure == | ||
Abbreviations are: | |||
* QC — Quantum-chemical calculations | |||
* GED — Gas electron diffraction | |||
* MW — Microwave spectroscopy | |||
* HRMS — High resolution molecular spectroscopy | |||
{| class="wikitable" | {| class="wikitable" | ||
| Line 10: | Line 16: | ||
|- | |- | ||
| ''r''<sub>e</sub> | | ''r''<sub>e</sub> | ||
| Equilibrium structure. | | Equilibrium structure. Appears as a result of Born-Oppenheimer approximation in quantum mechanics. | ||
| QC | | QC | ||
|- | |- | ||
| ''r''<sub>g</sub> | | ''r''<sub>g</sub> | ||
| Thermally averaged structure. | | Thermally averaged structure.<ref group="gt" name="tav">Interatomic distances are averaged over molecular vibrations for a given temperature. Generally such distances are geometrically inconsistent.</ref> ''r''<sub>g</sub> distances are centers of gravity for corresponding distribution functions ''P''(''r''). | ||
| GED | | GED | ||
|- | |- | ||
| ''r''<sub>a</sub> | | ''r''<sub>a</sub> | ||
| Average structure used for calculation of molecular scattering intensity. | | Average structure <ref group="gt" name="tav" /> used for calculation of molecular scattering intensity in GED theory. | ||
| GED | | GED | ||
|- | |||
| ''r''<sub>α</sub> = ''r''<sub>h0</sub> | |||
| Distances between average nuclear positions.<ref group="gt" name="tavnp">In contrast to ''r''<sub>g</sub>, where subject to averaging are interatomic distances, here atomic positions are averaged. Therefore this structure is geometrically consistent.</ref> | |||
| GED, MW, HRMS | |||
|- | |||
| ''r''<sup>0</sup><sub>α</sub>, ''r''<sub>z</sub> | |||
| Distances between average nuclear positions at 0 K, i.e. for ground vibrational state.<ref group="gt" name="tavnp" /> | |||
| GED, MW, HRMS | |||
|- | |||
| ''r''<sub>h1</sub> | |||
| Distances between average nuclear positions calculated taking into account nonlinear relationships between internal and Cartesian coordinates.<ref group="gt" name="tavnp" /> | |||
| GED, MW, HRMS | |||
|- | |||
| ''r''<sub>a3,1</sub> | |||
| Semi-experimental equilibrium structure obtained using corrections calculated by Shrink program utilizing cubic force fields. | |||
| GED, MW, HRMS | |||
|- | |||
| ''r''<sup>se</sup><sub>e</sub> | |||
| Semi-experimental equilibrium structure obtained using a set of theoretically calculated corrections to experimental and/or operational data. | |||
| GED, MW, HRMS | |||
|- | |- | ||
| ''r''<sub>s</sub> | | ''r''<sub>s</sub> | ||
| Line 27: | Line 53: | ||
| ''r''<sub>0</sub> | | ''r''<sub>0</sub> | ||
| Effective structure derived from rotational constants of zero-point vibrational level. | | Effective structure derived from rotational constants of zero-point vibrational level. | ||
| MW, HRMS | |||
|- | |||
| ''r''<sub>m</sub> | |||
| Effective structure derived from the mass-dependence method of Watson. | |||
| MW, HRMS | |||
|- | |||
| ''r''<sup>ρ</sup><sub>m</sub> | |||
| Effective structure similar to ''r''<sub>m</sub> obtained by a slightly modified method of Harmony et al. | |||
| MW, HRMS | | MW, HRMS | ||
|} | |} | ||
<references group="gt" /> | |||
Revision as of 11:49, 3 September 2015
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.