Raman spectra using laser

For gaseous TcF the IR spectrum was measured in the range from 6 to 43 pm [70] and the Raman spectrum using laser excitation [71 ]. The spectra were interpreted in terms of the octahedral point group O/, [72 [. Considerable broadening of the and / 2g fundamentals was observed for TcF and ReFf,. This broadening was attributed to dynamic Jahn-Teller coupling. The values of fundamental frequencies for technetium and rhenium hexafluoride arc Riven in Table 10.6.A. 

This spectrum is called a Raman spectrum and corresponds to the vibrational or rotational changes in the molecule. The selection rules for Raman activity are different from those for i.r. activity and the two types of spectroscopy are complementary in the study of molecular structure. Modern Raman spectrometers use lasers for excitation. In the resonance Raman effect excitation at a frequency corresponding to electronic absorption causes great enhancement of the Raman spectrum. 

Figure 5 Vibrational spectra of neat liquid acetonitrile (ACN) (top) mid-IR spectrum (bottom) Stokes Raman spectrum using a conventional spectrometer (solid line). The dashed spectrum obtained with the ultrafast laser system has somewhat lower resolution (From Ref. [46].)...

The 78S-nm line of the diode laser used in these experiments is transmitted voy efficiently by optical fibers. Moreover, this wavelength is ideal for measuring SER spectra of highly luminescent con unds that have visible absmption bands. This wavelength is far removed from most electronic absorption bands and thus produces little or no fluorescence. Furthermore, the spectral range of a typical Raman spectrum using 78S-nm excitation is within the range of photomultiplier tubes thus, diode lasers can be used with conventional spectrometers. 

Fia. 13. (a) Raman spectrum of a pretreated Cab-O-Sil disk recorded using a laser beam expander (b) infrared spectrum of a newly pressed Cab-O-Sil disk. From Hendra and Gilson, Laser Raman Spectroscopy, p. 186. Wiley, New York, 1970. 

Fig. 31 Evolution of the Raman spectra of a high-pressure and photo-induced sample of Se while decreasing the pressure at ca. 300 K [109]. The spectrum at 3.9 GPa shows the onset of the transformation S6 p-S. The asterisks indicate the Raman signals typical for p-S whereas the peaks of two stretching vibrations of p-S coincide with those of Se at about 458 cm and 471 cm (not indicated by asterisks). The Raman spectrum of the sample recovered at ambient pressure (0 GPa) is evidently a superposition of the spectra of a-Sg and polymeric sulfur, Sj, arrows indicate plasma lines of the Ar ion laser at 515 nm, which have been used for calibration). For Raman spectra under increasing pressure, see Fig. 23 in [1] and references cited therein...

Fig. 3 a UV-Vis DRS spectra of dehydrated TS-1 catalyst reporting the typical 208 nm (48000cm i) LMCT hand, see Fig. 2h also reported are the four excitation laser lines used in this Raman study near-lR (dotted), visible (full), near-UV (dashed) and far-UV (dot-dashed), b Raman spectra of dehydrated TS-1 obtained with four different lasers emitting at 7 = 1064,422,325, and 244 nm (dotted, full, dashed, and dot-dashed lines, respectively). Raman spectra have been vertically shifted for clarity. Although the intensity of each spectrum depends upon different factors, the evolution of the 7(1125)//(960) ratio by changing the laser source is remarkable. The inset reports the Raman spectrum collected with the 244 nm laser in its full scale, in order to appreciate the intensity of the 1125 cm enhanced mode. Adapted from [48] with permission. Copyright (2003) by The Owner Societies 2003... 

Raman spectroscopy is primarily useful as a diagnostic, inasmuch as the vibrational Raman spectrum is directly related to molecular structure and bonding. The major development since 1965 in spontaneous, c.w. Raman spectroscopy has been the observation and exploitation by chemists of the resonance Raman effect. This advance, pioneered in chemical applications by Long and Loehr (15a) and by Spiro and Strekas (15b), overcomes the inherently feeble nature of normal (nonresonant) Raman scattering and allows observation of Raman spectra of dilute chemical systems. Because the observation of the resonance effect requires selection of a laser wavelength at or near an electronic transition of the sample, developments in resonance Raman spectroscopy have closely paralleled the increasing availability of widely tunable and line-selectable lasers. 

Raman and resonance Raman (RR) measurements of fullerene-like particles of MoS2 recently have been carried out (93). By using 488-nm excitation from an Ar ion laser light source, the two strongest Raman features in the Raman spectrum of the crystalline particles, at 383 and 408 cm-1, which correspond to the E g and Aig modes, respectively (see Table I), were found to be dominant also in IF-MoS2... 

The thermal conductivity of suspended graphene has been calculated by measuring the frequency shift of the G-band in the Raman spectrum with varying laser power. These measurements yielded a value for thermal conductivity of 4840 5300 W m 1 K 1 [23], better than that of SWCNTs, with the exception of crystalline ropes of nanotubes, which gave values up to 5800 W m 1 K 1 [24]. Even when deposited on a substrate, the measured thermal conductivity is 600 W m 1 K 1 [25], higher than in commonly used heat dissipation materials such as copper and silver. 

The vibration-rotation gas-phase Raman spectrum of C3 O2 was obtained for the first time by Smith and Barrett using a 2-watt argon-ion laser. The results of this experiment gave new information about the bonding potential function for the central carbon bonding fundamental. 

With the available high-power lasers the nonlinear response of matter to incident radiation can be studied. We will briefly discuss as examples the stimulated Raman effect, which can be used to investigate induced vibrational and rotational Raman spectra in solids, liquids or gases, and the inverse Raman effect which allows rapid analysis of a total Raman spectrum. A review of the applications of these and other nonlinear effects to Raman spectroscopy has been given by Schrotter2i4)... 

However, the high frequency of the laser irradiation in the visible region may lead to photochemical reactions in the laser focus. Besides, fluorescence can often cover the whole Raman spectrum. Such problems can be avoided by using an excitation wavelength in the near-infrared (NIR) region, e.g. with an Nd YAG laser operating at 1064 nm. Deficits arising from the v dependence of the Raman intensity and the lower sensitivity of NIR detectors are compensated by the Fourier-Transform (IT) technique, which is widespread in IR spectroscopy . ... 

We conclude this chapter by presenting several examples of deconvolution of real data. Most of these examples represent deconvolutions of data that were used as part of a spectral analysis rather than generated as deconvolution examples or tests. The examples include high-resolution grating spectra, tunable-diode-laser (TDL) spectra, a Fourier transform infrared spectrum (FTIR), laser Raman spectra, and a high-resolution y-ray spectrum. 

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