Spectroscopy visible laser

New to the fourth edition are the topics of laser detection and ranging (LIDAR), cavity ring-down spectroscopy, femtosecond lasers and femtosecond spectroscopy, and the use of laser-induced fluorescence excitation for stmctural investigations of much larger molecules than had been possible previously. This latter technique takes advantage of two experimental quantum leaps the development of very high resolution lasers in the visible and ultraviolet regions and of the supersonic molecular beam. 

Vj = 1 <— v" = 1 transition will be at a different energy than the Vj = 0 <— v" = 0. We use this fact to measure the vibrational spectrum of V (OCO) in a depletion experiment (Fig. 12a). A visible laser is set to the Vj = 0 Vj = 0 transition at 15,801 cm producing fragment ions. A tunable IR laser fires before the visible laser. Absorption of IR photons removes population from the ground state, which is observed as a decrease in the fragment ion signal. This technique is a variation of ion-dip spectroscopy, in which ions produced by 1 + 1 REMPI are monitored as an IR laser is tuned. Ion-dip spectroscopy has been used by several groups to study vibrations of neutral clusters and biomolecules [157-162]. 

Of special Interest as O2 reduction electrocatalysts are the transition metal macrocycles In the form of layers adsorptlvely attached, chemically bonded or simply physically deposited on an electrode substrate Some of these complexes catalyze the 4-electron reduction of O2 to H2O or 0H while others catalyze principally the 2-electron reduction to the peroxide and/or the peroxide elimination reactions. Various situ spectroscopic techniques have been used to examine the state of these transition metal macrocycle layers on carbon, graphite and metal substrates under various electrochemical conditions. These techniques have Included (a) visible reflectance spectroscopy (b) laser Raman spectroscopy, utilizing surface enhanced Raman scattering and resonant Raman and (c) Mossbauer spectroscopy. This paper will focus on principally the cobalt and Iron phthalocyanlnes and porphyrins. 

Fig. 3.5. Experimental apparatus for time-resolved THz transmission spectroscopy. The sample is excited with a visible laser pulse delivered by delay line 3. A singlecycle THz electric-field transient probes the polarization response of the sample after time delay tv scanned by delay line 1. The transmitted THz amplitude is monitored via ultrabroadband electro-optic sampling in a THz receiver as a function of time T scanned by delay line 2. From [13]...

Room temperature ILs have been the object of several Raman spectroscopy studies but often ILs emit intensive broad fluorescence. In our own experiments, the use of visible laser light (green 514.5 nm or red 784 nm) resulted in strong fluorescence [29,46]. Similar observations have been reported for many IL sysfems. Our experimental spectra needed to be obtained by use of a 1064 nm near-IR exciting source (Nd-YAC laser at 100 mW of power). The scattered light was filtered and collected in a Bruker... 

The electrochemistry and cristallography of the nickel oxides have been extensively investigated in connection with the improvement of storage batteries . In-situ UV/visible reflectance spectroscopy and laser raman spectroscopy of the... 

It will not displace dispersive-visible laser Raman spectroscopy. 

The use of Raman spectroscopy in the lumber/paper industry has been found to be feasible using the FT-Raman technique. Earlier results using a visible laser were limited due to the laser-induced fluorescence created with most wood samples. Measures to circumvent fluorescence were time-consuming, and the signal-to-noise (S/N) ratio was poor. With most wood samples, using a near-IR laser excitation, fluorescence essentially was eliminated. 

Sources. The ultimate source for spectroscopic studies is one that is intense and monochromatic but tunable, so that no dispersion device is needed. Microwave sonrces such as klystrons and Gnnn diodes meet these requirements for rotational spectroscopy, and lasers can be similarly nsed for selected regions in the infrared and for much of the visible-ultraviolet regions. In the 500 to 4000 cm infrared region, solid-state diode and F-center lasers allow scans over 50 to 300 cm regions at very high resolution (<0.001 cm ), but these sources are still quite expensive and nontrival to operate. This is less trne... 

A review of CE and CZE by Haddad covers metallochromic ligands, dye ligands detectable by UY-visible spectroscopy or laser fluorescence for low detection limits (PAR, BrPADAP, XO, as shown in Figure 2) in CE and CZE separations.69... 

In principle, Raman microspectroscopy is attractive because the practical diffraction limit is on the order of the excitation wavelength, which is about 10-fold smaller for Raman spectroscopy with a visible laser than for mid-lR spectroscopy. It is therefore possible to focus visible or NIR laser light to much smaller spot... 

Visible lasers operating at much lower input power than the earlier gas lasers the most important of these is the He-Ne laser (632.8nm), while argon ion (488.0 and 514.5run) and krypton lasers (647.1, 568.2 and 530.9nm) are also useful for Raman spectroscopy. 

In the columns identifying the experimental method, MW stands for any method studying the pure rotational spectrum of a molecule except for rotational Raman spectroscopy marked by the rot. Raman entry. FUR stands for Fourier transform infhired spectroscopy, IR laser for any infiured laser system (diode laser, difference frequency laser or other). LIF indicates laser induced fluorescence usually in the visible or ultraviolet region of the spectrum, joint marks a few selected cases where spectroscopic and diffraction data were used to determine the molecular structure. A method enclosed in parentheses means that the structure has been derived from data that were collected by this method in earlier publications. The type of structure determined is shown by the symbols identifying the various methods discussed in section II. V/ refers to determinations using the Kraitchman/Chutjian expressions or least squares methods fitting only isotopic differences of principal or planar moments (with or without first... 

Application of 2D IR spectroscopy to PCET models of Section 17.3.2 is a logical starting point for this type of investigation. 2D methods can unravel the correlated nuclear motion in a PCET reaction and in principle decipher how vibrational coupling in the Dp/Ap interface couples to the ET event between the Ae/De sites. These data can identify the structural dynamics within the interface that promote PCET reactions in much the same way that local hydrogen bonding structure and dynamics mediate excited state PT reactions [239, 240]. In these experiments, the PCET reaction can be triggered by an ultrafast resonant visible laser pulse (as in a standard TA experiment) and a sequence of IR pulses may be employed to build a transient 2D IR spectrum. These experiments demand that systems be chosen so that the ET and PT events occur on an ultrafast timescale. 

This article is concerned with the developments in instrumentation and techniques in photochemistry and spectroscopy during the period July 1980— June 1981. Such a wide ranging topic is impossible to review at all critically, nor is it feasible to consider every publication concerning photochemical instrumentation. Consequently, many reports concerned merely with the application of established techniques have been omitted. In this respect, it should be noted that the relative brevity of some sections (for example plasma sources, u.v.-visible spectroscopy) in no way reflects the use or application of these techniques, but merely their advanced state of development. Further it is apparent that, during the past decade, a swing away from developments in instrumentation for conventional photochemistry in favour of spectroscopy and laser photochemistry has occurred. This has been reflected in the following discussion. The author would like to thank Dr. Mike West for several helpful discussions during the preparation of this manuscript. 

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