Zero audio frequency

Quadrature detection in t2 gives us two FIDs (real and imaginary) by sampling both the Mx component and the My component of the net magnetization as it precesses. This allows us to put zero audio frequency in the center of the spectral window and defines the left side... 

With quadrature detection, the range of audio frequencies detected runs from +SW/2 to -SW/2, with zero in the center. The same relationship exists between the maximum frequency detectable and the dwell time, except that we substitute SW for Fmax ... 

Both FIDs are acquired with the same t value, and both are encoded with the same frequency 2a in t, but they are 90° out of phase (cosine vs. sine modulation in t ), just as the real and imaginary channels of the receiver (Mx and My) are 90° out of phase. This gives us our quadrature detection in F, allowing us to put zero F audio frequency in the center of the F spectral window. 

The variable condenser connected in parallel with the variable resistance, / 3, serves to balance the capacity effects of the conductance cell. Adjustment of C and are made until the detector indicates zero voltage difference between points 1 and 3. In this condition of bridge balance the resistance Rc may be found from the expression 2 = R jRc- The position of balance may be indicated by a minimum signal on an oscilloscope or by minimum sound in earphones using audio frequency alternating voltage sources. 

The present chapter will cover detailed studies of kinetic parameters of several reversible, quasi-reversible, and irreversible reactions accompanied by either single-electron charge transfer or multiple-electrons charge transfer. To evaluate the kinetic parameters for each step of electron charge transfer in any multistep reaction, the suitably developed and modified theory of faradaic rectification will be discussed. The results reported relate to the reactions at redox couple/metal, metal ion/metal, and metal ion/mercury interfaces in the audio and higher frequency ranges. The zero-point method has also been applied to some multiple-electron charge transfer reactions and, wheresoever possible, these results have been incorporated. Other related methods and applications will also be treated. 

Optical frequency of the HeNe (15802.78 cm ) and the mirror velocity v is measured in cms . A typical mirror velocity for a FT-NIR spectrophotometer is v = 0.633 cms . The HeNe laser frequency is then modulated at 20 kHz, which puts the lower frequencies in the audio range where low-noise electronics are available to digitize and transform the signal. The detector response is measured at every zero-crossing of the HeNe laser signal. 

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