Kraitchman has shown that a single isotopic substitution on an atom is sufficient to determine directly the coordinates of that atom with respect to the principal axes of the original molecule. Kraitchman's formulas represent exact solutions of the equations for the equilibrium moments of inertia. However, the effects of the zero‐point vibrations are such that the coordinates obtained by substitution from the ground state moments of inertia I0 are systematically less than r0. These coordinates have here been called r (substitution) or rs, and it is found that rs≃(r0+re)/2, and Is= ∑ imirsi2≃(I0+Ie)/2.In the usual method of solution, the coordinate of one atom is determined from the equation for I0, and therefore the difference I0—Is must be made up by this one coordinate. This introduces a large error in the structures normally determined from ground state constants, and results in variations of 0.01 A in structures determined from different sets of isotopic species. If instead, we obtain the structure on...

Determination of Molecular Structures from Ground State Rotational Constants

A new criterion for the determination of molecular structures from ground state rotational constants

It is shown that the rotational energy levels of a symmetric‐top molecule can be classified according to symmetry species of the full symmetry group of the molecule. Useful selection rules for electric‐dipole transitions between rotational energy levels thus classified are presented. It is shown that the rotational energy levels can be labeled in addition by a convenient quantum number G, which is essentially a generalization of the +l, —l labels. Selection rules for this quantum number are presented, which, together with those for the symmetry species, allow one to determine easily the allowed branches for a transition between any two vibronic states in a symmetric‐top molecule.

Classification of Rotational Energy Levels for Symmetric‐Top Molecules

Lewis Acid Properties of Tris(pentafluorophenyl)borane. Structure and Bonding in L−B(C6F5)3 Complexes⊥

To date, 204 individual molecular species, comprised of 16 different elements, have been detected in the interstellar and circumstellar medium by astronomical observations. These molecules range in size from two atoms to seventy, and have been detected across the electromagnetic spectrum from cm-wavelengths to the ultraviolet. This census presents a summary of the first detection of each molecular species, including the observational facility, wavelength range, transitions, and enabling laboratory spectroscopic work, as well as listing tentative and disputed detections. Tables of molecules detected in interstellar ices, external galaxies, protoplanetary disks, and exoplanetary atmospheres are provided. A number of visual representations of this aggregate data are presented and briefly discussed in context.

https://iopscience.iop.org/article/10.3847/1538-4365/aae5d2/pdf

2018 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules

Microwave Spectra and Molecular Structures of Methyl Cyanide and Methyl Isocyanide

Microwave Determination of the Structure of Borine Carbonyl and of the Nuclear Moments of the Stable Boron Isotopes

The following nuclear and molecular constants have been obtained from microwave measurements of the pure rotational spectra of $\mathrm{ClCN} (J=2\ensuremath{\rightarrow}3 \mathrm{transition})$, $\mathrm{BrCN} (J=3\ensuremath{\rightarrow}4)$, and $\mathrm{ICN} (J=4\ensuremath{\rightarrow}5)$. The moments of inertia from the ground vibrational states are, in ${\mathrm{g}\ensuremath{-}\mathrm{c}\mathrm{m}}^{2}$ \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}40}$: for ${\mathrm{Cl}}^{35}$${\mathrm{C}}^{12}$${\mathrm{N}}^{14}$, ${140.5}_{11}$; for ${\mathrm{Cl}}^{35}$${\mathrm{C}}^{13}$${\mathrm{N}}^{14}$, ${141.2}_{45}$; for ${\mathrm{Cl}}^{37}$${\mathrm{C}}^{12}$${\mathrm{N}}^{14}$, ${143.4}_{80}$; for ${\mathrm{Cl}}^{37}$${\mathrm{C}}^{13}$${\mathrm{N}}^{14}$, ${144.2}_{83}$; for ${\mathrm{Br}}^{79}$${\mathrm{C}}^{12}$${\mathrm{N}}^{14}$, ${203.6}_{21}$; for ${\mathrm{Br}}^{81}$${\mathrm{C}}^{12}$${\mathrm{N}}^{14}$, ${204.7}_{86}$; for ${\mathrm{Br}}^{79}$${\mathrm{C}}^{13}$${\mathrm{N}}^{14}$, ${205.9}_{64}$; for ${\mathrm{Br}}^{81}$${\mathrm{C}}^{13}$${\mathrm{N}}^{14}$, ${207.1}_{72}$; for ${\mathrm{I}}^{127}$${\mathrm{C}}^{12}$${\mathrm{N}}^{14}$, ${260.0}_{99}$; and for ${\mathrm{I}}^{127}$${\mathrm{C}}^{13}$${\mathrm{N}}^{14}$, ${264.0}_{72}$. The interatomic distances in A for the ground vibrational states are ${d}_{\mathrm{CCl}}=1.630$, ${d}_{\mathrm{CN}}=1.163$, for ClCN; ${d}_{\mathrm{CBr}}=1.789$, ${d}_{\mathrm{CN}}=1.160$, for BrCN; and ${d}_{\mathrm{CI}}=1.995$, ${d}_{\mathrm{CN}}=1.159$, for ICN. Quadrupole couplings in mc/s evaluated from the hyperfine structure are: for ${\mathrm{Cl}}^{35}$, -83.5; for ${\mathrm{Cl}}^{37}$, -65.0; for ${\mathrm{Br}}^{79}$, 686; for ${\mathrm{Br}}^{81}$, 573; and for ${\mathrm{I}}^{127}$, -2420.

Harold Ring

Papers

Microwave Spectra and Molecular Structures of Methyl Cyanide and Methyl Isocyanide

Microwave Determination of the Structure of Borine Carbonyl and of the Nuclear Moments of the Stable Boron Isotopes

Interatomic Distances and Nuclear Quadrupole Couplings in ClCN, BrCN, and ICN

Nuclear Quadrupole Coupling of Nitrogen in ICN and N 2 O

Microwave Spectra: Methyl Cyanide and Methyl Isocyanide