Radiofrequency spectrum

If the radiofrequency spectrum is due to emission of radiation between pairs of states for example nuclear spin states in NMR spectroscopy the width of a line is a consequence of the lifetime, r, of the upper, emitting state. The lifetime and the energy spread, AE, of the upper state are related through the uncertainty principle (see Equation 1.16) by... 

Figure 8.4. Six-line radiofrequency spectrum of ortho-H2 (J = 1) observed in a magnetic field of 1611 G, obeying the selection rules AM/ = 1, AMj = 0, observed by Kolsky, Phipps, Ramsey and Silsbee [4]. The original spectrum was recorded manually point by point as shown.

The electron spin-spin constant kv is not determined directly through the radiofrequency spectrum, but nevertheless plays a very important role, as does also the rotational constant Bv. In both cases the required values were taken from the optical electronic spectrum. 

One of the most interesting and important results of the study was to show how the molecular constants change as the vibrational quantum number v increases. This behaviour is presented in table 8.10. The electron spin-spin and rotational constant values came, initially, from the analysis of the optical electronic spectrum [47], although the values of the spin-spin constants for different vibrational levels were refined by the analysis of the radiofrequency spectrum. The nuclear hyperfine parameters are obtained solely from the magnetic resonance experiments. We will discuss the significance of these constants in the following subsection. 

A particularly fascinating aspect of the radiofrequency spectrum shown in figure 8.49 is the anomalous position of the v = 4 resonance, to which we referred above. Gammon, Stern and Klemperer [168] made a careful study of this effect, which... 

Memorandum, OTSG, SGPS-PSP, 13 January 1994, subject The Sub-Radiofrequency Spectrum (Static to 3 kHz Band). 

The radiofrequency spectrum of phosphine has been measured in a molecular beam electric resonance spectrometer. The suspected inversion doubling was not observed its dipole moment (ju.) was 0.574 D. The calculated rotational barrier between the staggered and eclipsed conformers of methylphosphine is 1.83 and 1.71 kcal mol, in agreement with the experimental value of 1.96 from microwave measurements. An orbital-by-orbital analysis of the changes which occur upon rotation suggests a hydrogen-bond contribution when the phosphorus lone pair of electrons and a CH bond are appropriately orientated.The existence of a 1—2° tilt of a methyl group towards the phosphorus lone pair of electrons in methylphosphines (138) was a conclusion drawn from a microwave study... 

Originally the radiofrequency spectrum of the output voltage of the optical mixing photomultiplier tube was analyzed with a swept filter... 

Indium Halides.— The radiofrequency spectrum of In F has been unsuccessfully examined with the aim of finding an electric hexadecapole interaction of the indium nucleus (the upper limit for any such interaction was 2 kHz). 7... 

The a n state of CO was first identified through its ultraviolet emission spectrum to the ground state, producing what are now known as the Cameron bands [ 160, 161, 162]. Its radiofrequency spectrum was then described by Klemperer and his colleagues in a classic series of molecular beam electric resonance experiments. Its microwave rotational spectrum was measured by Saykally, Dixon, Anderson, Szanto and Woods [163], and the far-infrared laser magnetic resonance spectrum was recorded by Saykally, Evenson, Comben and Brown [164]. In the infrared region both electronic... 

A part of the UHF radiofrequency spectrum from 1 to 2 GHz is by the IEEE terminology called the L-band and the D-band according to the NATO terminology. Its advantages are adequate to physical propagation characteristics. The band has tolerable free space loss and the Earth atmosphere signal... 

The essential features of an NMR spectrometer shown m Figure 13 5 are not hard to understand They consist of a magnet to align the nuclear spins a radiofrequency (rf) transmitter as a source of energy to excite a nucleus from its lowest energy state to the next higher one a receiver to detect the absorption of rf radiation and a recorder to print out the spectrum... 

FID Free induction decay, decay of the induction (transverse magnetisation) back to equilibrium (transverse magnetisation zero) due to spin-spin relaxation, following excitation of a nuclear spin by a radio frequency pulse, in a way which is free from the influence of the radiofrequency field this signal (time-domain) is Fourier-transformed to the FT NMR spectrum (frequency domain)... 

Figure 2. Partial 100 MHz P.M.R. Spectrum of 3,4,6-tri-O-acetyl-v-glucal (1) measured for a chloroform -d solution (A normal spectrum of the Hi and H2 resonances respectively (B) frequency sweep spin-decoupled spectrum of the Hi and H2 resonances, with a strong decoupling field centred on the Hs resonance (C), as in (B) above, but with an additional weak radiofrequency field centred on the high field transition of the H2 resonance (D), as in (B) above, but with a weak radiofreauency field centred on the low field transition...

A homonuclear spin-system may be excited with radiofrequency (r.f.) pulses that are so Intense (in the order of p.s), compared to the frequency width of the spectrum, that all resonances are excited essentially uniformly. This is a nonselective excitation. A homonuclear spin-system may also be excited with a relatively weak, r.f. pulse (in the order of ms), in the sense that all components of a given multiplet are inverted at time zero, whereas the other resonances in the spectrum remain essentially unperturbed this is a selective excitation. The r.f. pulse may be single-selective, that is, there is an inversion of one multiplet in the spectrum, or double-selective, triple-selective, and so on, where two, three, or more separate multiplets in the spectrum are inverted simultaneously while the remaining resonances remain unperturbed. 

Continuous wave A method of recording an NMR spectrum in which the field B] is applied continuously and either the magnitude of Bo or the radiofrequency is varied so that the nuclei are brought successively into resonance. 

Fig. 5.3.8 Photograph of the detection region of the NMR probe with radiofrequency coil. A methane—air mixture was ignited above the zeolite pellets. The mixture also contained xenon for NMR detection. Hp-129Xe NMR spectra with 30% xenon (from high-density xenon optical pumping) in 70% methane is depicted. (1) The spectrum in the absence of combustion and (2) the spectrum during combustion. Adapted from Ref. [2],...

---