Ammonia rotational spectrum

From its inception, microwave rotational spectroscopy has contributed greatly to our knowledge about classical inorganic compounds. It all began with a low resolution recording of the ammonia inversion spectrum in 1934. The first high resolution microwave spectra were recorded... 

Bloemink, H. I., Hinds, K., Holloway, J. H., and Legon, A. C., Characterization of a pre-reac-tive intermediate in gas-phase mixtures of fluorine and ammonia The rotational spectrum of the H N—F complex, Chem. Phys. Lett. 245, 598-604 (1995). 

The most important example of the kind of molecule just discussed is ammonia, NHg. That it is actually a symmetrical top molecule is made plausible by the fact that some, but not all, of its vibration-rotation bands are of the simple three-branch type while the pure rotation spectrum confirms this view. The non-vanishing dipole moment as well as the presence of this latter spectrum exclude the possibility of three H-atoms in the form of an equilateral triangle with the N-atom in the same plane at the centre. There remains then the symmetrical pyramidal form discussed above and a plane configuration... 

Lightman A., Ben-Reuven A. Line mixing by collisions in the far-infrared spectrum of ammonia, J. Chem. Phys. 50, 351-3 (1969) Cross relaxation in the rotational inversion doublets of ammonia in the far infrared, J. Quant. Spectrosc. Radiat. Transfer 12, 449-54 (1972). 

Fig. 17. Energy levels of the rotation-inversion spectrum of ammonia. The quantum numbers (J,K) are given for each level. The heavy arrows indicate the inversion transitions detected in interstellar space and their frequencies in MHz. Thin arrows indicate the rotation-inversion transitions located in the submillimeter wave region. Dashed arrows indicate some collision induced transitions...

These early papers, as well as most of the theoretical work on the inversion of ammonia that has been done later, have considered the problem of the solution of the Schrddinger equation for a double-minimum potential function in one dimension and the determination of the parameters of such a potential function from the inversion splittings associated with the V2 bending mode of ammonia Such an approach describes the main features of the ammonia spectrum pertaining to the V2 bending mode but it cannot be used for the interpretation of the effects of inversion on the energy levels involving other vibrational modes or vibration—rotation interactions. 

Evidently the rotational lines are split depending on the value of the constant D lf. In the rotational Raman spectrum of ammonia NH3 this /f-splitting could be resolved (Cloppenburg et al., 1979). 

Olthof, E. H. T., van der Avoird, A, and Wormer, R E. S., Structure, internal mobility, and spectrum of the ammonia dimer Calculation of the vibration-rotation tunneling states, J. Chem. Phys. 101, 8430-8442 (1994). 

Hydrazine bears the same relation to ammonia as hydrogen peroxide to water. That the molecule is similar to hydrogen peroxide is shown by the Raman spectrum and high dipole moment (1.83 D) of the monomeric vapour. Like the hydroxyl groups in hydrogen peroxide, (p. 381) the NHg-groups in hydrazine are without free rotation. 

Mierowave studies in moleeular beams are usually limited to studying the groimd vibrational state of the complex. For eomplexes made up of two molecules (as opposed to atoms), the intermolecular vibrations are usually of relatively low amplitude (though there are some notable exceptions to this, such as the ammonia dimer). Under these eireumstances, the methods of classical microwave spectroscopy can be used to determine the structme of the complex. The principal quantities obtained from a microwave spectrum are the rotational constants of the complex, which are conventionally designated B and C in decreasing order of magnitude there is one rotational constant B for a linear complex, two constants (A and Bor B and C) for a complex that is a symmetric top and three constants (A, B and C) for an... 

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