Infrared lasers

Another situation in which an already well-studied proton transfer reaction serves as a probe of a physical phenomenon has been suggested by Knight, Goodall and Greenhow (43, 44). They ionized water with single photons of Nd glass laser infrared radiation and measured an ion recombination rate constant for the reaction... 

A number of anomeric D-hex-2-ulopyranosyl azides have been synthesized and their photochemistry examined. For both a- and P-azides, the major photoproducts arise from cleavage of the C-2C-3 bond and migration of the C-3 carbon to the nitrene centre. Decomposition reactions of a glycidyl azide polymer have been induced by pulsed laser infrared pyrolysis and UV photolysis of thin films at 17-77 K and monitored by IR spectroscopy. The initial step is elimination of N2 and formation of imines, which decompose on warming, possibly with secondary polymerization. 

Niedziela, R.F., M.L. Norman, C.L. DeForest, R.E. Miller and D.R. Worsnop A temperature- and composition-dependent study of H2SO4 aerosol optical constants using Fourier transform and tunable diode laser infrared spectroscopy, J. Phys. Chem. A 103 (1999) 8030-8040. 

The techniques used in these experiments have several features tant for the study of the decomposition of energetic materials. First, the excitation step using the CO2 laser infrared multiphoton absorption provides a way of heating the molecule under isolated conditions. After an initial coherent multiphoton absorption step, the infrared photons are sequentially absorbed, proceeding through the high density of states legton... 

On-site TP winding requires heat and pressure to consolidate the RP heat sources include lasers, infrared and quartz lamps, induction heating shoes and hot gas torches. The consolidation pressure can be applied either by fiber tension or by mechanical devices. On-site winding is being used in the USA for reinforcement and refurbishment of structures such as... 

Some of these ions (diatomic cations CH", NH, OH" and HpO ") have been studied through their electronic spectra prior to the present activity of molecular ion spectroscopy. We use laser infrared spectroscopy infrared because all these ions absorb infrared radiation strongly and laser spectroscopy because of its hi sensitivity and resolution. 

Height relative to reference (laser, infrared or ultrasonic sensor)... 

Figure 9 (A) Spectral stripping of components from the tunable diode laser infrared spectrum of cigarette smoke. From bottom to top ethylene, acrolein, methanol, and comparison with hydrazine. The reference spectrum is the lower of the two traces in each case. (B) Expanded view of the residual spectrum compared to that of hydrazine. (Reprinted with permission from Plunkett S, Parrish ME, Shafer KH, Nelson D, Shorter J, and Zahniser M (2001) Time-resolved analysis of cigarette combustion gases using a dual infrared tunable diode infrared laser system. Vibrational Spectroscopy 27 53-63 Elsevier.)...

For reading the temperature as an in-process control a non-contact laser infrared digital thermometer is used. The consistency could be measured using two glass plates as a simple extensometer. 

The term upconversion describes an effect [1] related to the emission of anti-Stokes fluorescence in the visible spectral range following excitation of certain (doped) luminophores in the near infrared (NIR). It mainly occurs with rare-earth doped solids, but also with doped transition-metal systems and combinations of both [2, 3], and relies on the sequential absorption of two or more NIR photons by the dopants. Following its discovery [1] it has been extensively studied for bulk materials both theoretically and in context with uses in solid-state lasers, infrared quantum counters, lighting or displays, and physical sensors, for example [4, 5]. Substantial efforts also have been made to prepare nanoscale materials that show more efficient upconversion emission. Meanwhile, numerous protocols are available for making nanoparticles, nanorods, nanoplates, and nanotubes. These include thermal decomposition, co-precipitation, solvothermal synthesis, combustion, and sol-gel processes [6], synthesis in liquid-solid-solutions [7, 8], and ionothermal synthesis [9]. Nanocrystal materials include oxides of zirconium and titanium, the fluorides, oxides, phosphates, oxysulfates, and oxyfluoiides of the trivalent lanthanides (Ln ), and similar compounds that may additionally contain alkaline earth ions. Wang and Liu [6] have recently reviewed the theory of upconversion and the common materials and methods used. 

Letokhov, V. S., and Ryabov, E. A. (2004). Laser infrared multiphoton noncoherent control of intermolecular (isotope) selectivity for polyatomic molecules on a practical scale. Israel Journal of Chemistry, 44, 17. 

Localized chemical processes, such as desorption and ablation, stimulated by resonant laser pulse-surface layer interaction have been discovered recently. In this lecture the essential theoretical features of the desorption induced by resonant excitation of adsorbate vibrations with laser infrared and their influence on yield, rate, and quantum efficiency are presented. Results on selective damage to pigmented biological structures by short resonant optical and ultraviolett laser pulses are briefly reported. 

Very fast energy dissipation after vibrational excitation in the electronic ground state, however, has been inferred from picosecond relaxation measurements on large molecules in the gas phase. Moreover the view has been adopted that in solids even at low temperature rapid energy dissipation prevents multiphoton excitation and vibrational ladder climbing in matrix isolated molecules. On the other hand, in recent experiments surface reactions, such as desorption, evaporation and molecular decomposition, stimulated by vibrational multi-quantum excitation with resonant laser infrared have been observed at moderate threshold laser intensity and with high frequency selectivity. 

A laser infrared pulse striking a surface covered with an adsorbate can pump energy into... 

In principle, also a laser infrared pulse should be able to deposit sufficient energy into the vibration of the adsorptive bond so that the molecule desorbs. However, the vibration of the adsorptive bond will be very enharmonic, particularly at high excitation, so that desorption induced by monochromatic infrared will be very unlikely, except at enormous laser intensities, calculated to be in the order of >10 Wcm". (3) In addition there must be considerable broadening of the vibrational energy levels of the adsorptive bond. Then process (2) is of little resonant character. In general process (3), the direct interaction between the adsorbent and laser infrared, will heat up the system leading to thermal desorption. This is particularly true for metals, where extremely fast relaxation of electronic excitation into the phonon bath within lO s takes place. Laser induced thermal desorption is possible at all laser frequencies at which appreciable absorption of light occurs in the adsorbent.(4)... 

Let us consider process (1) in which laser infrared is resonantly coupled into an internal vibration of the adsorbed molecule followed by desorption. This process has been investigated in the systems CH3F on NaCl, SF5 on NaCl by Heidberg et al. (5,1) and for pyridine on KCl and silver by Chuang et al.(6) It has been theoretically treated in an illuminating way by Kreuzer and coworkers (7) and Ewing and coworker.(8) We shall partly adopt Kreuzer s description of the CH F-NaCl experiment. According to the experiment the frequency of the internal vibration of the adsorbed mole-... 

Fig. 5.9.1 A spectmm of the R(ll) line of ethane on Jupiter recorded with a CO2 laser infrared heterodyne spectrometer. LO marks the frequency of the laser local oscillator. The observed 25 MHz spectmm (histogram) was detected with a 64-channel radio frequency receiver at the output of the infrared detector mixer. The dashed and solid curves are calculations of the line shape (Kostiuk et al, 1987).

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