A. Givan

Fourier transform infrared and Raman studies on solid nitrogen dioxide: Temperature cycling of ordered, disordered, and multicomponent layers

Fourier transform infrared (FTIR) spectra of nitrogen dioxide layers deposited at various rates and substrate temperatures, are reported. Bands assignable to N2O4(D2h) (ordered and disordered layers), to O=N–O–NO2 ‘‘D’’ and ‘‘D’’’ isomers, to NO+NO−3 nitrosonium nitrate and to the NO2 monomer were observed. The relative amounts of species depends upon deposition conditions. Temperature cycling effects were followed up to 205 K. Solid N2O4(D2h) behaves like a normal, stable molecular solid, its disordered layer exhibiting small frequency shifts, but also being stable with respect to temperature cycling. The observation of NO+NO−3 bands is related to the existence of the D’ isomer and of monomeric NO2. Raman experiments overemphasize the NO+NO−3 form due to resonant enhancement.

The infrared and Raman spectra of matrix isolated binary and mixed mercury halides

Raman and ir spectra in the stretching region of all HgX2 and HgXY molecules (X,Y=Cl, Br, I) trapped in solid Kr at 20 °K are reported. Bands are assigned to modes of monomers and dimers. Bond stretching and interaction force constants are calculated and compared. The possibility of a slightly bent structure for several monomers is indicated. The dimer structure is shown to be centrosymmetric in all cases and the identity of the bridged halogen is suggested for the ’’mixed’’ dimers.

Matrix isolation infrared and Raman spectra of binary and mixed group II B fluorides

Infrared and Raman spectra of all MF2 and MFX molecules (M=Zn, Cd, Hg; X=Cl, Br) and the infrared spectrum of the fluoroidide HgFI isolated in solid krypton at 20 °K are reported. The MFX species were formed in a vapor mixture of the appropriate MF2 and MX2 dihalides, vaporized, at different temperatures, from separate compartments of a double‐oven crucible. The spectra are the first experimental evidence for the existence of the molecular fluorohalides. All three fundamentals of the MF2 molecules and the two stretching mode frequencies of the MFX molecules are assigned. Harmonic force constants are evaluated and isotope effects are used to discuss their geometry. Thermodynamic functions are tabulated for the binary difluorides.

Matrix isolation infrared and Raman spectra of binary and mixed zinc dihalides, isotopic effects, force constants, and thermodynamic properties

Raman and infrared matrix solution spectra for all ZnX2 and ZnXY (X,Y=Cl,Br,I) molecules are reported. These spectra complete the vibrational information on the binary dihalides and provide the first experimental evidence for the existence of the mixed zinc dihalides. All three fundamentals are assigned for all molecules. Isotopic effects due to the halogen atoms, the zinc atoms, or both were resolved in the stretching mode bands. From these, stretching, bending, and interaction force constants were evaluated, the criterion for their calculation being the reproduction of band frequencies within experimental error and the best fit of the frequency differences in the resolved isotopic fine structures. The possibility that not all molecules are linear is indicated. The effect of temperature and deviations from linearity on calculated entropies is shown.

On the intermolecularity or intramolecularity of nitrosonium nitrate formation in thin films of nitrogen dioxide: a Fourier transform infrared study

The question of whether the formation of the NO+NO−3 (nitrosonium nitrate), the ionic form of nitrogen dioxide, via the decomposition of the ON–O–NO2, ‘‘D’’’ isomer, is an inter‐ or intramolecular process, is addressed via temperature and concentration dependent FTIR studies of mixed films of N2O4 with CCl4. The process of nitrosonium nitrate production, both during deposition of disordered solid films of nitrogen dioxide and during their subsequent warming, is concluded to be intermolecular but not order dependent. A mechanism is tentatively suggested.

Fourier transform infrared study of amorphous N2O4 solid: Destabilization with inert impurities

Amorphous N2O4 solid was formed on predeposited oxygen or krypton layers. Evaporation of the underlying layer and redeposition of the inert impurities resulted in decomposition of the ionic nitrosonium nitrate clusters within the solid nitrogen tetroxide. Infrared features indicate NO+NO−3 decomposition to occur via molecular NONO3 , with NO2 monomers as products. Evaporation of the inert impurities and recooling restored the amorphous N2O4 from which NO+NO−3 was formed again.

The infrared and Raman spectra of matrix isolated binary and mixed mercury halides. II. Extension to low frequencies

The vibrational investigation of all matrix isolated HgX2 and HgXY (X,Y=Cl, Br, I) molecules has been extended to the bending mode region. The use of an auxiliary third monochromator (TTM) in Raman experiments reduced background scattering down to low frequencies, previously inaccessible. All ν2 frequencies are reported, standard entropies evaluated, and bending force constants calculated. The possibility of slightly bent structures, especially for HgBrI, as formerly discussed on the basis of stretching force constant trends, is reinforced. Irregularities in relative intensities of the stretching mode bands of the mixed dihalides are interpreted in terms of differences in electronegativity of the halogens. Several observations are also made on nonmonomeric bands.

Raman studies on molecular and ionic forms in solid layers of nitrogen dioxide: Temperature and light induced effects

Raman spectra of zero pressure formed N2O4 solid layers are reported. Sample composition is extremely dependent upon deposition conditions. For ordered and pure solid N2O4(D2h), produced by slow NO2 deposition, temperature cycling over the range in which the solid is stable shows no significant spectral changes and does not result in autoionization, as argued in a previous Raman study. Fast and low temperature deposited layers are amorphous and multicomponent, showing bands of disordered and isomeric molecular N2O4 and of ionic NO+NO−3, nitrosonium nitrate. For nitrosonium nitrate, three solid modifications (two crystalline, one amorphous) can be characterized spectroscopically. In the amorphous phase, a light induced, temperature dependent, reversible transition between molecular and ionic nitrogen tetroxide is observed below 150 K. The paths leading to nitrosonium nitrate formation are examined.

Fourier transform infrared spectrum of well ordered solid dinitrogen tetroxide

The full infrared spectrum of well ordered N2O4(D2h) thin films is reported. Improved sample crystallinity is reflected in a fine structure of the internal mode bands that is less complicated than previously reported, and in a well resolved phonon spectrum. New assignments, notably for the v10(B2u) internal deformation mode, are suggested and the symmetry classification of the phonon bands is substantiated.

The vibron–phonon sidebands in the Fourier‐transform infrared spectra of the molecular crystal CO2

FTIR investigations on polycrystalline CO2 at various temperatures show Stokes and anti‐Stokes sidebands coupled to the vibrational modes v3, v2, and v+/v− (Fermi dyad). The latter is infrared forbidden and may be eliminated from spectra of good quality polycrystalline films. The main peaks in the structure of the sidebands may be assigned to phonons from points of highest symmetry in the Brillouin zone. The vibron–phonon coupling process is mode specific and driven by electrical anharmonicity in case of v+ and v−. For the infrared allowed fundamentals, and especially at the Γ point, the coupling process is also driven by mechanical anharmonicity. The dispersion of these internal modes at k=0 influences the coupled phonons and thus the one phonon density of states is correctly mirrored by the v+ and v− sidebands only.