Double vibrational absorption

The apparatus used to perform vibrational relaxation experiments in supercritical fluids consists of a picosecond mid-infrared laser system and a variable-temperature, high-pressure optical cell (68,73). Because the vibrational absorption lines under study are quite narrow (<10 cm-1), a source of IR pulses is required that produces narrow bandwidths. To this end, an output-coupled, acousto-optically Q-switched and mode-locked Nd YAG laser is used to synchronously pump a Rhodamine 610 dye laser. The Nd YAG laser is also cavity-dumped, and the resulting 1.06 pm pulse is doubled to give an 600 u.l pulse at 532 nm with a pulse duration of "-75 ps. The output pulse from the amplified dye laser ("-35 uJ at 595 nm, 40 ps FWHM) and the cavity-dumped, frequency-doubled pulse at 532 nm... 

The cis isomer of 9-cycloheptadecenone will show a more intense double-bond absorption in the IR spectrum, due to the greater change of its dipole moment with vibration. The trans isomer has no net dipole moment, and will show comparatively little absorption intensity. Also, the trans isomer will snow a characteristic band at... 

Vibrational Absorption of Interfacial and Double-layer Species... 

Vibrational Absorption of Species outside the Double-layer... 

Infrared IR spectroscopy is quite useful in identifying carboxylic acid derivatives The, carbonyl stretching vibration is very strong and its position is sensitive to the nature of IKT the carbonyl group In general electron donation from the substituent decreases the double bond character of the bond between carbon and oxygen and decreases the stretch mg frequency Two distinct absorptions are observed for the symmetric and antisym metric stretching vibrations of the anhydride function... 

Since IR spectra are essentially due to vibrational transitions, many substituents with single bonds or isolated double bonds give rise to characteristic absorption bands within a limited frequency range in contrast, the absorption due to conjugated multiple bonds is usually not characteristic and cannot be ascribed to any particular grouping. Thus IR spectra afford reference data for identification of pyrimidines, for the identification of certain attached groups and as an aid in studying qualitatively the tautomerism (if any) of pyrimidinones, pyrimidinethiones and pyrimidinamines in the solid state or in non-protic solvents (see Section 2.13.1.8). 

Vibrationally mediated photodissociation (VMP) can be used to measure the vibrational spectra of small ions, such as V (OCO). Vibrationally mediated photodissociation is a double resonance technique in which a molecule first absorbs an IR photon. Vibrationally excited molecules are then selectively photodissociated following absorption of a second photon in the UV or visible [114—120]. With neutral molecules, VMP experiments are usually used to measure the spectroscopy of regions of the excited-state potential energy surface that are not Franck-Condon accessible from the ground state and to see how different vibrations affect the photodissociation dynamics. In order for VMP to work, there must be some wavelength at which vibrationally excited molecules have an electronic transition and photodissociate, while vibrationally unexcited molecules do not. In practice, this means that the ion has to have a... 

Recent work in our laboratory has shown that Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRRAS) can be used routinely to measure vibrational spectra of a monolayer on a low area metal surface. To achieve sensitivity and resolution, a pseudo-double beam, polarization modulation technique was integrated into the FT-IR experiment. We have shown applicability of FT-IRRAS to spectral measurements of surface adsorbates in the presence of a surrounding infrared absorbing gas or liquid as well as measurements in the UHV. We now show progress toward situ measurement of thermal and hydration induced conformational changes of adsorbate structure. The design of the cell and some preliminary measurements will be discussed. 

The EMIRS and SNIFTIRS methods provide the IR vibrational spectra (really the difference spectra - see later) of all species whose population changes either on the electrode surface or in the electrical double layer or in the diffusion layer in response to changing the electrode potential. Spectra will also be obtained for adsorbed species whose population does not change but which undergo a change in orientation or for which the electrode potential alters the Intensity, the position or shape of IR absorption bands. Shifts in band maxima with potential at constant coverage (d nax 6 very common for adsorbed species and they provide valuable information on the nature of adsorbate/absorbent bonding and hence also additional data on adsorbate orientation. 

Infrared spectra of unsaturated organotin epoxides show absorption bands at 1235 and 850 cm-1, which are typical of epoxy groups, 3085 and 1640 cm-1 (double bonds) and in the range 510-585 cm-1 (Sn—C bonds). Symmetrical deformation vibrations of the CH3 or CH2 group that is closest to the tin atom are related to changes of H—C—H angles and appear in the 1190-1175 cm-1 range 31). 

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