A systematic investigation has been carried out of the vibrational spectra of the hydrogen peroxide crystal and its deutorated analogue, using both i.r. and Raman spectroscopy, over the range 4000-50 cm-1. Mixtures of the two isotopic species up to approximately 95 ~o deuteration were also studied to identify the fundamentals of the hybrid molecule, HDO 2. Single crystals of hydrogen peroxide oriented along two of the three crystallographic axes were examined in the Raman effect with polarized laser light. The O-H stretching bands are remarkably narrow in the Raman spectra: Av(½) = 20 cm-1 at-193°C compared with about 80 cm-1 in the i.r. Nearly all the O-H stretching components predicted by the factor group analysis were observed but a satisfactory identification of all components of the OOH deformation modes could not be achieved. The O-O stretching frequency in D20 z (872 cm-1) is slightly higher than in HzOz (871 cm-1) contrary to expectations. The hydrogen bonds in the HzOz crystal appear somewhat less strong (by about 10-15 ~o) than those in ice. A normal coordinate analysis of the unit cell modes proved to be of considerable value in the assignment of observed frequencies. The values of the eleven principal force constants and the twenty interaction constants used to fit the 59 assigned frequencies appear reasonable and are comparable with values found for other hydrogen bonded systems.
The fundamental skeletal vibrations of the H2O3 and H2O4 molecules and their deuterated analogs have been identified in the infrared or Raman spectra of the trapped products from reactions in electrically dissociated water vapor and related systems. All the observed frequencies have been assigned on the basis of assumed molecular structures of C2 symmetry, consisting of skew chains of single-bonded oxygen atoms with an OH group at each end. The assignments are consistent with the temperature behavior, 18O isotope shifts, and depolarization ratios of the various bands. Some unusual isotope effects were found in the deuterated species. A preliminary normal coordinate analysis of the skeletal vibrations of H2O3 and H2O4, including their 18O isotopic species, shows satisfactory agreement of the calculated and observed frequencies, thereby supporting the assumed molecular model. It also confirms that the bonding in these very unstable molecules is similar to that in H2O2.
Further study by Raman spectroscopy of the condensed products from electrically dissociated water vapor and other related systems has revealed the presence, not only of ozone in appreciable amounts, but also of molecular oxygen in still greater amounts trapped at 80 OK. The concentration of ozone relative to the hydrogen oxides varied somewhat with experimental conditions, and also locally due to some segregation effect in the glassy condcnsate. The concentration of trapped oxygen showed still wider fluctuations depending particularly on surface effects in the discharge-flow system. On warming up under vacuum the intensity of the Oz and O3 bands began to decrease even before the crystallization temperature was reached (about 150 OK), thereby confirming that the gas evolution at that stage is mainly a desorption process. Therefore, the often quoted ratio of total evolved Oz to residual H z 0 2 could not be a reliable index of the formation of hydrogen polyoxides, H z 0 3 and H 2 0 4 , in these systems. A mechanism is proposed for the formation in situ of the trapped gases and in particular, for a source of oxygen atoms in dissociated water vapor.The fundamental vibrations of the ozone n~olecule, v, = 1106, v2 = 703, and v3 = 1036 cm-I, were confirmed by polarization and isotope shift measurements.
The vibrational spectra of the addition compound Na2C2O4.H2O2 show mutual exclusion of all the fundamentals in infrared (i.r.) and Raman. This feature is confirmed by a study of the partly deuterated compound. It agrees with the conclusion of a previous X-ray and nuclear magnetic resonance study that the hydrogen peroxide molecule in that crystal is planar and centrosymmetric. The two component molecules are held together by strong (9 kcal mole−1) hydrogen bonds. Some 20 lattice modes were detected in i.r. or Raman. For comparison purposes, the lattice spectra of anhydrous sodium oxalate were also investigated.
The i.r. and laser Raman spectra of pure, crystalline Caro's acid, H2SO5, were measured for the first time between 4000 and 30 cm−1. Most of the fundamental vibrations of the molecule could be identified by comparison with those of the H2SO4, H2O2 and HSO5− species. In addition, a dozen or so of lattice modes were recorded. The O—O stretching frequency is slightly higher (886 cm−1) than in solid H2O2, contrary to expectation. The two hydroxyl groups are quite different, both chemically (Caro's acid is essentially monobasic) and spectroscopically. The ionizable OH group forms strong intermolecular hydrogen bonds, as in H2SO4. However, the non-ionizable O2H group is engaged mainly in intramolecular hydrogen bonding. The unit cell of the crystalline acid must contain more than two molecules.
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