Spectroscopic constants table, diatomics

Table 2.6. Exchange-only spectroscopic constants of diatomic molecules Self-consistent KLl [51] versus HF [55,56] results...

Table 2 Observed spectroscopic constants and calculated potential constants for a selection of diatomic molecules 1... 

In practice, the result of the perturbation treatment may be expressed as a series of formulae for the spectroscopic constants, i.e. the coefficients in the transformed or effective hamiltonian, in terms of the parameters appearing in the original hamiltonian, i.e. the wavenumbers tor, the anharmonic force constants , the moments of inertia Ia, their derivatives eft , and the zeta constants These formulae are analogous to equations (23)—(27) for a diatomic molecule. They are too numerous and too complicated to quote all of them here, but the various spectroscopic constants are listed in Table 3, with their approximate relative orders of magnitude, an indication of which parameters occur in the formula for each spectroscopic constant, and a reference to an appropriate source for the perturbation theory formula for that constant. 

Table 14.1 lists spectroscopic constants for some common diatomic molecules. These are taken from several sources and are of varying accuracy. The National Institute of Standards and Technology (NIST) maintains an extensive online compendium of spectroscopic and other chemical data at http // webbook.nist.gov/chemistry/. Spectroscopic constants are expressed in MHz and GHz rather than cm" .To convert units, note that v(cm ) = v(Hz)/c where c is the speed of light. A useful relation is... 

This table lists the leading spectroscopic constants and equilibrium internuclear distance in the ground electronic state for selected diatomic molecules. The constants are those describing the vibrational and rotational energy through the expressions ... 

The Franck-Condon factors (FCFs) for the strongest bands of a band system are located in a (v, v") table such that a parabola (the Condon locus) often tracks through them [1-3]. The tilt of this parabola, and its latus rectum, can be calculated from the spectroscopic constants of the upper and lower electronic states of the transition. It is relatively rare that the spectroscopic constants and the FCFs are available for any given molecule the availability is most common for isoelectronic sequences. Hence, we calculate these two properties for the Condon loci of similar band systems for the molecules in isoelectronic sequences. The hypothesis of the work is that these loci will manifest the periodicities of the constituent atoms in the diatomic molecules. 

The value Cqo cannot be obtained by measurement of transition frequencies because it does not show up in an energy difference (AE) equation. It contributes, usually in a small way, to the zero-point energy of the system. Table 9.1 lists spectroscopic constants of a number of diatomics. 

Some spectroscopic constants obtained for a few selected diatomic molecules are collected in Table XV. Information on the vibrational constants can also be obtained from the rotational constants, for example. 

Table 6-2 lists spectroscopic constants for a number of diatomic molecules. The values are given in wavenumbers (cm ) as this is a convenient unit for infrared spectroscopy. 

Table 6-2. Spectroscopic constants for a number of diatomic molecules are listed. The values are obtained from Reference [1] in the bibliography section at the end of this chapter. The term Do refers to the dissociation energy of the molecule.

Bourcier, S., Spectroscopic Data Relative to Diatomic Molecules, vol. 17 of Tables of Constants and Numerical Data, Pergamon, New York, 1970. A comprehensive collection of experimental data. 

B. Rosen, Spectroscopic Data Relative to Diatomic Molecules , International Tables of Selected Constants, Pergamon Press, Oxford, 1971, Vol. 17. 

Applications.—Diatomic Molecules. Spectroscopic methods provide much more precise information on diatomic molecules—the equilibrium bond length, re, and the harmonic and anharmonic potential constants— than electron diffraction measurements can at present supply. In addition, the theory interrelating the different types of bond-length parameter is very simple for diatomic molecules. Thus electron diffraction studies of diatomic molecules serve mainly as a test of electron diffraction technique. Accurate studies have been carried out for Nj, O2," NO, Clj, and I2." Typical results are shown in Table 3. 

Table 3 Comparison of electron diffraction and spectroscopic determinations of re for some diatomic molecules. Spectroscopic potential constants were used in the conversion of the electron diffraction r to re-Spectroscopic re values from reference 2d. For diatomic molecules (only) it is more convenient to compare re values. All distances in A...

Diatomic Molecules. For triatomic molecules there are terms involving Coriolis interactions between vibrational modes in the correction from Bg to Bz, and the theory of the preceding sections is required. For linear or for bent symmetrical XY, molecules the rotational constants of a single isotopic species are sufficient to define the molecular structure completely, and thus for such molecules spectroscopic methods are superior in precision to the electron diffraction method. Electron diffraction studies serve as a test not only of the electron diffraction technique but also of the comparability between and r%. Some examples are given in Table 4. Besides the molecules CS., CIO, and CO, for which details are given, a... 

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