Vapor-phase IR spectrum

The Coriolis coupling constant ( 3 = 0.74 could be derived from the OP,RS branch separation (21.9 cm ) of Vas(GeC) in the vapor phase Raman spectrum. But 3 == 0.17 resulted from the P,R branch separation (16.3 cm ) of the same vibration in the vapor phase IR spectrum [68]. Calculations based on known geometrical data gave a P,R branch separation of 17.9 cm and the rotational constant A = 0.095 cm [98]. Coriolis constants were also calculated by approximation formulas ( 3 0.22) giving estimates of the OP,RS branch separation and the... 

Infrared spectra of polymers are also obtained in a rapid screening mode by pulse pyrolysis-FTIR using solid samples (ca. 0.1-0.5 mg) that are placed "as is" into the Pyroprobe-Pyroscan-FTIR system for semi-quantitative, qualitative information. The vapor phase IR spectrum in Figure 3a is that from a pulse pyrolysis (750 C for 10 sec) of a 100 mg sample of solid poly(styrene). The thermal decomposition of poly(styrene) to its slyrene... 

Figure 3. Pyrolysis FTIR. (a) Vapor phase IR spectrum of poly(styrene) pulse pyrolyzed at 750 C/10 sec. (b) TimsHosolved l rolysis-FTIR spectrum of CI-PVC (60 C/min to 900 C). (c) HCI vapor phase FTIR spectrum (3500-2500 cm-1) firam CI-PVC pyrolysis (60 C/min to 900 C in helium), (d) Time-resolved Pyrolysis-FTIR spectrum of ethylene-vinyl acetate copolymer (60 C/min to 900 C in helium).

The kinetics of epoxidation were measured in situ as the rate of uptake of olefin by the catalyst, since the epoxide product remains adsorbed on the catalyst surface in the absence of solvent. Addition of 2 Torr cyclohexene vapor (30 pmol) to a 14.2 mg sample of 3 (9.0 pmol Ti, 4.5 pmol V) at room temperature resulted in the loss of the o(C=C) mode in the gas phase IR spectrum over the... 

This PLOT separation allowed vapor-phase IR and mass spectral determinations to be made. Figure 7 shows a typical IR spectrum obtained from Peak X in the above FFAP chromatogram. The spectrum corresponds to a 6-sec scan with computer background correction and normalization. The spectral features correspond well with an alkyl phenolic structure and a comparison spectrum is shown in Figure 8 for 2,4-dimethylphenol eluted from the FFAP column under identical condi-... 

Chromium(VI) tetrafluoride oxide (mp 55°) is a dark red solid that exists in equilibrium with its purple vapor at 25°. It is highly soluble in BrFj, SO2CIF, and anhydrous HF. The gas-phase IR spectrum has a very strong characteristic absorption band at 755 cm assigned to 77(6). Medium absorption bands are at 1028 Vi(Ai) and at 696 72( 1)cm . The mass spectrometric cracking pattern is CrOF, CrOF, CrOF, CrF, CrOF", CrO, and Cr. ... 

The thermal decomposition of 2 results in the formation of only two main products, which could be identified using IR spectroscopy, namely CO2 [94] and CO [95]. In addition trace amounts of HCN and CH4 were visible in the gas-phase IR spectrum, however, no evidence for the formation of water vapor was foimd. fii the methylated compounds, many more decomposition products were observed using gas-phase IR spectroscopy. Besides CO2 and CO, larger amounts of CH4 [96] and HCN were found in the decomposition of 5 and 6, in comparison with 2. In contrast to 5, where bigger amounts of expected NH3 were detected, the thermal decomposition of 6 shows only traces of NH3 but moderate amoimts of N2O [97]. 

Several manufacturers offer GC-FT IR instruments with which a vapor-phase spectrum can be obtained on nanogram amounts of a compound eluting from a capillary GC column. Vapor-phase spectra resemble those obtained at high dilution in a nonpolar solvent Concentration-dependent peaks are shifted to higher frequency compared with those obtained from concentrated solutions, thin films, or the solid state (see Aldrich, 1985). 

The IR spectra of the chemicals are measured in the vapor phase, as the GC effluent is hot. One of the problems associated with the spectrum measurement in the gas phase is that a gas-phase spectrum of a chemical differs considerably from those measured in other phases. See Section 3.3 for further discussion on this subject. 

Certain functional groups in a molecule (e.g., hydroxyl, carbonyl, and amine) absorb IR radiation and exhibit absorption bands at characteristic frequencies regions regardless of the structure of the rest of the molecule. These bands are termed group frequencies. They are predictable and allow the analyst to deduce important structural information about an unknown molecule. An IR spectrum can be rapidly recorded for any phase, i.e., solid, liquid, or vapor. By coupling IR spectroscopy with other analytical techniques such as nuclear magnetic resonance (NMR)... 

In addition to transitions in the ir manifold discussed above, some attention has been given recently to possible o-ir states in the ultraviolet nonradlative transitions from the B2jj state. Callomon et al. (27) have postulated the transitions from higher vibrational levels of B2y to a E2u(high resolution absorption spectrum of vapor phase benzene in the 5.0 eV region. initio (12,28) calculations have predicted the presence of at least one a state (e2 ) lying between two filled ir-molecular orbitals. Photoionization (29,30) experiments, and other evidence (31) appear to agree with the conclusion that a-o-ir transition may be... 

IR and Raman spectra were recorded and assigned for 1,3-dioxolane (24) and a range of mono-, di- and trimethylated derivatives at an early date <59JCS807>. IR data for l,3-dioxolan-2-one (25) in solid, liquid, solution and vapor phases and its Raman spectrum have also been reported <56TFS1 178, 68JSP(27)285>, as have both IR and Raman spectra for l,3-dioxol-2-one (8) <70JST(5)67>. Other simple... 

Fig. 3. (a) Infrared spectrum of poly 2-hydroxyethyl methacrylate (PHEMA) on a salt (date glued into a gas phase IR cell, (b) Spectrum alter exposure to d4 methanol vapor. Arrows indicate major peaks moved by deu-teration... 

Cyclohexene was dried and vacuum-distilled before use. It was degassed by three freeze-punp-thaw cycles and stored over activated molecular sieves in a glass bulb. It was introduced into the reactor via vapor phase transfer through a high vacuum manifold (base pressure <10 Torr). After 30 mins, the epoxide yield was quantified on an HP 6890 GC/MS equipped with a J W Scientific DBl capilary column. At the end of each experiment, Ti analysis was performed (15) and epoxide/Ti ratios were calculated. For kinetics experiments, silica powder containing the /ert-butylperoxotitanium complex was prepared in an in situ reactor and the reaction initiated by addition of olefin. The IR spectrum of the gas phase above the silica was recorded at timed intervals. Pseudo-first-order rate constants... 

The rate of expoxidation was measure in situ via the uptake of cyclohexene vapor by the catalyst. At low pressures (ca. 10 Torr), cyclohexene does not adsorb on the unmodified silica surface nor on either of the silica-supported 2-alkoxide conplexes 1 and 3. However, the addition of cyclohexene vapor to 2 resulted in a rapid, exponential loss of v(C=C) intensity in the IR spectrum of the gas phase above the silica-supported complex. Figure 2. We infer that epoxidation results in adsorption of cyclohexene oxide on the catalyst surface. 

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