Frequency scanning experiments

In conventional nanosecond pump-probe dispersive TRIR experiments, also described previously, kinetic data are collected at one frequency at a time. These data can then be used to construct a series of time-resolved IR spectra. Thus, in the dispersive experiment kinetic data are used to construct spectra, and in the step-scan experiment spectral data are used to derive kinetics. 

Fig. 2.11. Correct adjustment of the pulse frequency offset vq (a) and maladjustment (b). In (b) the signal at 144.1 ppm is folded to <5 < 125 ppm. Sample 90% ethylbenzene in hexadeuteriobenzene at 20 MHz single scan experiments with 90" pulses.

Equations (16) and (17) describe second-harmonic generation (SHG) and third-harmonic generation (THG) of one laser beam with a single polarization. Self-phase modulation (SPM) of a single laser beam is described in Eq.(18) as e.g. employed in z-scan experiments [6]. Equation (19) is the cross-phase modulation (XPM) process between two laser beams and Eq.(20) describes the four wave mixing with degenerate frequencies (DFWM). 

The addition of an electromagnetic shield to the body of the tip can greatly reduce the stray capacitance. This is particularly useful for fast-scan voltammetry [54] and high frequency impedance experiments [55],... 

At York University, Toronto, microwave measurements have been revived by Storry and Hessels [9,10], that could benefit of lasers to excite the 23P level, instead of the lamps used by Hughes and coworkers. Also, the detection of laser-induced fluorescence from 23P levels makes another basic difference with respect to Hughes experiments, which, together with a microwave frequency scan, eliminated the lineshape asymmetries. In this experiment, a moderate magnetic field is also used to select the transitions between the desidered Mj sublevels. The... 

The TICA specimen preparation procedure has been described elsewhere (4). The mechanical measurements were made with the Rheometrics Mechanical Spectrometer (RMS) which measures the in-phase and out-of-phase stress response (a and b component respectively) of a specimen being subjected to a sinusoidal shear strain. The instrumental set-up was reported by Lee (6). The frequency of the strain function was kept constant at 1.6 Hz (10 rad/sec). All temperature scan experiments were scanned at 2 C/min rate. The temperature was scanned down at the same rate when the maximum temperature was reached. 

The frequency dependence of the loss peak in a temperature scanning experiment indicates whether it arises from viscoelastic relaxation or is associated with chemical reaction. One would expect a peak associated with a viscoelastic relaxation to occur at higher temperatures at higher frequencies, which is true for the lowest and highest temperature peaks observed (Figure 13). ... 

Simultaneous account for local field and local density of photon states enhancements in close proximity to a silver ellipsoidal nanopaiticle is found to provide up to 10 -fold Raman scattering cross-section rise up. A model of the so-called hot points in surface enhanced spectroscopy has been elaborated as local areas with high Q-factor at incident and scattered (emitted) light frequencies. Further experiments are proposed towards verification of the model in terms of transient Raman experiments to clarify incident field enhancement and scanning near-field optical mapping of local density of photon states. 

In step scan FTIR the moving mirror. Mm, is moved incrementally in discrete steps. There are two main types of step scan experiment (i) time-domain step scan and (ii) frequency-domain or... 

The 983 analyser can be programmed to measure a sample s viscoelastic characteristics at up to 57 frequencies during a single test. In such multiplexing experiments, an isothermal step method is used to hold the sample temperature constant while the frequencies are scarmed. The sample is allowed to reach mechanical and thermal equilibrium at each frequency before the data are collected. After all the frequencies have been scanned, the sample is automatically stepped to the next temperature and the frequency scan is repeated. Multiplexing provides a more complete rheological assessment than is possible with a single frequency. 

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