Sequential excitation

Fortunately, an alternative method of excitation exists, instead of the sequential excitation of nuclei by the slow variation of the magnetic field. This involves the application of a short but intense radiofrequency pulse extending over the entire bandwidth of frequencies in which the nuclei to be observed resonate, so that all the nuclei falling within the region are excited simultaneously. As a result the total scan time is made independent... 

Due to Eq. (A.3) the above theories only permit the excitation of one quantum of vibration at a time (b and b+ connect vibrational states where their populations differ by only one quantum). This is a consequence of the linear approximation because the nuclear coordinates deviate slightly from the equilibrium situation the molecule can only change its vibrational state by the smallest of the allowed quantities one quantum. In order to account for the excitation of several quanta at a step (coherent excitation) one needs to use other kind of theories (see for example [24]). Nevertheless, the presented approaches permit the sequential excitation of quanta in a ladder climbing fashion (incoherent excitation). 

A different perspective of the vibrational structure of the Sj electronic state is illustrated in Figure 2.13b. This is an OODR that was obtained by sequentially exciting CI2CS with two photons of different colors. In this experiment, a photon from the first laser (the pump photon) induces a Si <— So vibronic transition that is followed after a short time delay by a second S2 Si, probe photon that carries the excitation to the S2 state. The pump laser is advanced to the blue and interrogates the bands of the S2 <— So system while the probe laser is scanned at the same rate to the red such that the total energy matches a selected vibrational level of the S2 state. In this way, an excitation spectrum of the vibrational band structure of the S2 state is constructed by monitoring the fluorescence that originates from the S2 state. 

The next species considered for transfer pumping by NF(a) was Bh, o. 44, 45 j jiis molecule was an attractive candidate for several reasons. BH can be sequentially excited to the A H state (Tq = 23073.9 cm ) by two near resonant transfer steps. It may be obtained by decomposition of volatile inorganic precursors, which was thought to be an advantage because these materials and their decomposition products would probably be... 

M12. Mitchell, D. G., and Johansson, A., Simultaneous multielement analysis using sequentially excited atomic fluorescence radiation. Specirochim. Acta, Part B 25, 175-182 (1970). 

Note that the case for emission of a blue photon by Tm3+ is slightly different than that of Er ". A three-step process is indicated. This may consist of excitation of the Tm3+ ion and energy transfer from two excited Yb3+ ions, or excitation of the Tm3+ ion by exchange (sequential excitation) with three excited Yb3+ sites. Note that two relaxation steps (phonon emission to the host lattice) would be Involved. 

Indicator-mediated optrodes frequently have an optical isolation at the fiber tip to prevent ambient light and sample from interfering in the optical system, and a fairly constant tip chemistry with its almost invariable refractive index (see Figure 18-11). However, as with plain fiber sensors, additional discriminations such as pulsed excitation plus electronic background subtraction or sequential excitation are useful techniques for improving selectivity. 

Plain fibers also have been used to perform in vivo measurements of drugs in minute volumes of body fluid by using conventional methods of absorptiometry [48] and fluorimetry [49], but also more sophisticated methods such as two-photon-excited fluorimetry and sequentially excited fluorimetry [49]. Detection limits of ca O.S pmol/L were determined for the drug adriamcin (doxorubicin) in interstitial fluid and whole blood and are comparable for the three... 

The magnitude of the interactions in ESR, exceeding that in NMR by several decades, makes pulsed excitations rather difficult. Consequently, most dynamic ESR studies are performed as continuous wave (CW) experiments, employing a sequential excitation of the spin system. It can be shown, however, that the frequency spectra from the CW technique are identical with those obtained by FT of the FID, following a single pulse [45, 65, 7. ... 

PRACTICE EXAMPLE B By using a two-photon process (that is, two sequential excitations), a chemist is able to excite the electron in a hydrogen atom to the 5d level. Not all excitations are possible they are governed by selection rules (see Are You Wondering 8-6). Use the selection rules to identify the possible intermediate levels (more than one are possible) involved, and calculate the frequencies of the two photons involved in each process. Identify the transitions allowed when a sample of hydrogen atoms excited to the 5d level exhibits an emission spectrum. When a sample of gaseous sodium atoms is similarly excited to the 5d level, what would be the difference in the emission spectrum observed ... 

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