Two-Dimensional Attenuated Total Reflection Infrared and Near-Infrared Correlation Study of the Structure of Butyl Alcohol/Water Mixtures

The effect of temperature on attenuated total reflection infrared (ATR-IR) and near-infrared (NIR) transmission spectra of pure butan-1-ol, butan-2-ol, 2-methyl-propan-1-ol, 2-methyl-propan-2-ol, and mixtures with a small water content (XH2O ≤ 0.1) have been examined. The spectra were analyzed using a two-dimensional (2D) correlation approach. Two kinds of correlation analysis were performed: IR–IR and NIR–NIR homo-correlation and IR–NIR hetero-correlation. Our results reveal that the addition of small to moderate amounts of water does not destroy the structure of alcohol. The presence of water stabilizes the structure of alcohols and this effect is more evident for sec-butanol and tert-butanol. The ATR-IR spectra provide information on the most associated species, whereas absorption of the smaller associates and the free OH group is hardly seen. On the contrary, in the NIR spectra the absorption of the free OH groups dominates. The ability of resolution enhancement in the hetero-correlation asynchronous spectra is reduced as compared to that in the homo-correlation spectra. On the other hand, peaks may appear in the hetero-correlation synchronous spectra that are not observed in the homo-correlation contour plots. The positions of the synchronous peaks were used for evaluation of anharmonicity constants. These values for the free OH group do not depend on the experimental conditions. In contrast, the anharmonicity constants for the bonded OH groups determined from the spectra of pure alcohols may significantly differ from those obtained from diluted solutions.

Laser Induced Fluorescence From CF2 Excited at 248 Nm

KrF–laser-induced fluorescence from CF2-radicals was investigated during photolysis of CF2Cl2 and CF2HCl by 193 nm laserlight. In contrast to other publications, which postulated single-vibronic-level fluorescence, the fluorescence is caused by excitation from four closely situated absorption bands. These fluorescence bands of four series, are assigned to Ã1B1(v′1,6−2v′1,0) − X˜1A1(v″1,v″2,0) transitions with Δv1=0 and 0 ≤ v″2 ≤ 30. The Franck – Condon factors of the Ã1B1 (0, 6, 0) –X˜1A1 (0, v″2, 0) transitions, the frequencies of the bending vibration (ω″2 =673± 2cm–1) and the anharmonicity constants x″22 = –0.94 ± 0.08 cm-1 and x′22 = –0.44 ± 0.10 cm–1 were more precisely determined. For the first time higher anharmonicity constants are evaluated with x″12 + x″112 = –3.5 ± 1.0 cm–1 and x″122= –0.05 ± 0.02 cm–1.

High Resolution FTIR Study of the ν8 Band and ab initio Calculation of the Harmonic and Anharmonic Force Field of Difluoromethanimine, CF2NH

The ν8 band of CF2NH near 830 cm-1 has been measured with a resolution of 0.003 cm-1 and rotationally analyzed. The band is unperturbed, and its rovibrational parameters are given up to fourth order. Theoretical harmonic and anharmonic force constants have been calculated at the 6-31 G **SCF level, and all vibration-rotation interaction constants αi and anharmonicity constants xij are predicted. The theoretical results are compared with the available experimental data

High Resolution Proton Energy Loss Spectroscopy of High Overtone Levels of Polyatomic Molecules

In the inelastic scattering of nearly monoenergetic proton beams (≅ 20 e V) from polyatomic molecules such as CF4 sharp peaks are observed corresponding to the excitation of very high overtone levels (n ≤ 14) of the infrared active modes. The collision mechanism leading to the high degree of excitation is described and an example from recent experiments is presented. A fit of the CF4 spectra provides new anharmonicity constants for the ν3-mode.

Vibrational properties of surface hydroxyls: Nonempirical model calculations including anharmonicities

Complete sets of harmonic, semidiagonal cubic as well as diagonal cubic and quartic force constants are reported for the internal coordinates of terminal, ≣SiOH, and bridging, ≣SiOH·Al≣, surface hydroxyls on silica and zeolites. They are obtained by numerical differentiation of analytically calculated gradients of the energy (SCF approximation, 6-31 G* basis set). A GF vibrational analysis is performed and after making a nonlinear transformation of the force constants into normal coordinates the anharmonicity constants are evaluated by perturbation theory. Comparison is made with the D2OH+ ion and the DOH molecule. The calculated anharmonicities of the OH bonds in the systems studied are remarkably constant and vary between -76 and -84 cm-1, only in agreement with the values observed for DOH (-83 cm-1) and surface silanols, ≣SiOH (-90 ± 15 cm-1).