Ground state transitions, microwave

Microwave spectroscopy is generally defined as the high-resolution absorption spectroscopy of molecular rotational transitions in the gas phase. Microwave spectroscopy observes the transitions between the quantised rotational sublevels of a given vibrational state in the electronic ground state of free molecules. Molecular... 

From a study of the microwave spectrum of 2-methylselenophene, the second-order Stark effect in the ground state was determined.11 The technique used was double radiofrequency-microwave resonance. For the identification by the double resonance method transitions of chiefly the A-state were chosen. From these observations the components of the dipole moment of 2-methylselenophene and the total dipole moment were determined. 

Specific microwave effects can be expected for polar mechanisms, when the polarity is increased during the reaction from the ground state towards the transition state (as more or less implied by Abramovich in the conclusion of his review in 1991 [42]). The outcome is essentially dependent on the medium and the reaction mechanism. 

These reactions are among the most propitious for revealing specific microwave effects, because the polarity is evidently increased during the course of the reaction from a neutral ground state to a dipolar transition state. 

This microwave effect is consistent with the fact that the rate-determining step may be certainly the generation of aldimine A from aldehydes and 2-amino 3-pico-line. It is in agreement with the transition state develops a dipole and, consequently more polar than the ground state. To ascertain this hypothesis, it was effectively next shown that the reaction involving reaction with preformed aldimine A, no revealed any microwave effect [119]. 

Recently, it has been postulated that the increase of the polarity of the reaction system (i.e., either development or increase of dipole moment) from the ground state (GS) towards the transition state (TS) can result in an acceleration of the reaction due to a stronger interaction of microwaves with the reagents during the course of the reaction. Thus, non-thermal microwave effect can be expected for the reaction with polar mechanisms when the stabilization of the transition state (TS) is more effective than that of the ground state (GS), which results in an enhancement of the reactivity as a result of the decrease in activation energy (Fig. 2.3) [36]. 

Fig. 1. Muonium energy levels for states with principal quantum numbers n = 1 and n = 2. The indicated transitions could be induced to date using modern techniques of microwave or laser spectroscopy. High accuracy has been achieved for the indicated transitions which involve the ground state. The atoms can be produced very efficiently only in the Is state...

Abstract. Following a suggestion of Kostelecky et al. we have evaluated a test of CPT and Lorentz invariance from the microwave spectrosopy of muonium. Precise measurements have been reported for the transition frequencies U12 and 1/34 for ground state muonium in a magnetic field H of 1.7 T, both of which involve principally muon spin flip. These frequencies depend on both the hyperfine interaction and Zeeman effect. Hamiltonian terms beyond the standard model which violate CPT and Lorentz invariance would contribute shifts <5 12 and <5 34. The nonstandard theory indicates that P12 and 34 should oscillate with the earth s sidereal frequency and that 5v 2 and <5 34 would be anticorrelated. We find no time dependence in m2 — vza at the level of 20 Hz, which is used to set an upper limit on the size of CPT and Lorentz violating parameters. 

Several molecules with 3 A. ground states have been studied by both microwave and far-infrared laser magnetic resonance they include O2, SO and SeO. In O2 the observed transitions are necessarily magnetic dipole, and they are frequently used to calibrate the sensitivity of a FIR laser magnetic resonance spectrometer. The other species have electric dipole transitions, and we shall illustrate the situation by describing the studies of SO carried out by Carrington, Levy and Miller [56], SO was also one of the first free radicals to be studied by pure microwave methods, which we will describe in chapter 10. The analysis of the magnetic resonance spectrum actually made use of the parameters determined earlier by pure microwave studies. SO is an easy radical to study experimentally since it is relatively unreactive and has a lifetime of several... 

There can be no question that the most important species with a 3 E ground state is molecular oxygen and, not surprisingly, it was one of the first molecules to be studied in detail when microwave and millimetre-wave techniques were first developed. It was also one of the first molecules to be studied by microwave magnetic resonance, notably by Beringer and Castle [118]. In this section we concentrate on the field-free rotational spectrum, but note at the outset that this is an atypical system O2 is a homonuclear diatomic molecule in its predominant isotopomer, 160160, and as such does not possess an electric dipole moment. Spectroscopic transitions must necessarily be magnetic dipole only. 

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