The Stark Effect of the Ammonia Inversion Spectrum

Coles, Donald K.; Good, William E.; Bragg, J. K.; Sharbaugh, A. H.

doi:10.1103/physrev.82.877

Cited by 57 publications

(7 citation statements)

References 5 publications

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“…Ammonia has a substantial dipole moment of 1.47 D, [90] reasonably approximated by computations at the CCSD(T) level of theory. [91] Of course, NH 3 forms moderately strong hydrogen bonds which are important in determining the phase diagram of this molecule.…”

Section: Hydrogen Bondingmentioning

confidence: 75%

A Molecular Perspective on Lithium–Ammonia Solutions

2009

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A detailed molecular orbital (MO) analysis of the structure and electronic properties of the great variety of species in lithium-ammonia solutions is provided. In the odd-electron, doublet states we have considered: e-@(NH3)n (the solvated electron, likely to be a dynamic ensemble of molecules), the Li(NH3)4 monomer, and the [Li(NH3)4+.e-@(NH3)n] ion-pairs, the Li 2s electron enters a diffuse orbital built up largely from the lowest unoccupied MOs of the ammonia molecules. The singly occupied MOs are bonding between the hydrogen atoms; we call this stabilizing interaction H-->H bonding. In e-@(NH3)n the odd electron is not located in the center of the cavities formed by the ammonia molecules. Possible species with two or more weakly interacting electrons also exhibit H-->H bonding. For these, we find that the singlet (S=0) states are slightly lower in energy than those with unpaired (S=1, 2...) spins. TD-DFT calculations on various ion-pairs show that the three most intense electronic excitations arise from the transition between the SOMO (of s pseudosymmetry) into the lowest lying p-like levels. The optical absorption spectra are relatively metal-independent, and account for the absorption tail which extends into the visible. This is the source of Sir Humphry Davy's "fine blue colour" first observed just over 200 years ago.

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Section: Hydrogen Bondingmentioning

confidence: 75%

A Molecular Perspective on Lithium–Ammonia Solutions

2009

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“…, µ the permanent electric dipole moment (1.468 Debye, Coles et al 1951), g I the spin statistical weight [4 for quantum number K = 3n (ortho-NH 3 ), 2 for K = 3n (para-NH 3 ), where n is an integer; for details see Townes and Schawlow (1975) and Kroto (1992)], f the beam filling factor, N the column density, Q the partition function, E u the energy of the upper state [23.4 K, 64.9 K, 124.5 K, and 202.3 K for the (1, 1), (2, 2), (3, 3), and (4, 4) lines, respectively] (e.g., Ho, Townes 1983), and T rot the rotational temperature. The rotational partition function (Q) can be expressed as…”

Section: Results and Analysismentioning

confidence: 99%

Observations of Ammonia in External Galaxies I. NGC 253 and M 82

Takano

Nakai

Kawaguchi

2002

Publications of the Astronomical Society of Japan

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The ammonia (J, K) = (1, 1), (2, 2), (3, 3), and (4, 4) transitions in the 23.7-24.1 GHz region were searched for in nearby galaxies, NGC 253 and M 82, to study the relation between the molecular abundances and physical conditions. The (1, 1), (2, 2), and (3, 3) emission lines were clearly detected in NGC 253, but no lines were found in M 82. In NGC 253 the shapes of the three emission lines were different from one another. The rotational temperatures obtained in NGC 253 were 17-50 K, depending on the velocity components. There are two main results: (1) The ortho-to-para abundance ratio was obtained in NGC 253 and found to be different depending on the velocity components. The ratio was about 1 for the velocity component where the (2, 2) line is detected. On the other hand, the ratio was more than 6 for another velocity component where the (2, 2) line is barely detected. This high ratio corresponds to an equilibration temperature of less than 8 K between ortho and para. (2) The abundance of NH 3 in NGC 253 was found to be about an order of magnitude larger than the upper limit in M 82. This result is an additional evidence for the different molecular abundances which were already reported between NGC 253 and M 82. In addition, the molecular abundances including NH 3 in nearby galaxies with rich molecular gas were compared, and we found that the molecular abundance in M 82 is systematically peculiar concerning the formation mechanisms of molecules. We discussed factors which cause such a peculiarity in M 82.

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“…It should be noted that these parameters were not fitted to the particle spectra. 21,24,25,[27][28][29][30][31][32][33][34][35][36][37] Dipole ͑ z ͒ and quadrupole ͑⍜ zz ͒ moments are reproduced by construction as are bending frequencies ͑ 2 , 4 ͒ and the symmetric stretching fundamental ͑ 3 ͒. Table II compares several monomer, dimer, and bulk properties calculated with the above model potential with corresponding experimental or theoretical ͑high level ab ini-tio͒ reference values.…”

Section: A Model Potentialmentioning

confidence: 99%

Size effects in the infrared spectra of NH3 ice nanoparticles studied by a combined molecular dynamics and vibrational exciton approach

Firanescu

Luckhaus

Signorell

2006

The Journal of Chemical Physics

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Infrared extinction spectra of ammonia ice nanoparticles with radii between 2 and 10 nm show pronounced band shape variations depending on the conditions of particle formation by collisional cooling. We present experimental and theoretical evidence showing that the variations in the region of the nu2 (umbrella) fundamental are due to changes in the particle size. The effect is analyzed in terms of an explicit atomistic model of the particles' structure and vibrational dynamics. An explicit potential function combined with a novel extension of the vibrational exciton approach allows us to simulate extinction spectra for particles containing up to 16,000 atoms. It is shown that the particles formed under the conditions of our experiments consist of a crystalline core surrounded by an amorphous shell with an approximately constant thickness of 1-2 nm. For the nu2 fundamental, this shell gives rise to a broad band [full width at half maximum (FWHM) 72 cm(-1)] blueshifted by about 19 cm(-1) relative to a narrow peak (FWHM of 19 cm(-1)) which arises from the crystalline core.

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The Stark Effect of the Ammonia Inversion Spectrum

Cited by 57 publications

References 5 publications

A Molecular Perspective on Lithium–Ammonia Solutions

A Molecular Perspective on Lithium–Ammonia Solutions

Observations of Ammonia in External Galaxies I. NGC 253 and M 82

Size effects in the infrared spectra of NH3 ice nanoparticles studied by a combined molecular dynamics and vibrational exciton approach

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