Triple-resonance spectroscopy

A second example, mentioned already, is microwave spectroscopy of Rydberg levels that have been exited by resonant two-step absorption of two-dye lasers (Fig. 10.36b). The high accuracy of microwave spectrosopy allows the precise determination of finer details, such as field-induced energy shifts of Rydberg levels, broadening of Rydberg transitions by black-body radiation or other effects, which might not be resolvable with optical spectroscopy. 

Problem 10.1. A linearly polarized laser beam passes in z-direction through a sample cell. Its wavelength is limited to a transition l) 2) with Ji 0, J2 1. With the laser 

Problem 10.2. Assume the absorption cross section a = lO cm for a linearly polarized laser with E D. What is the angular distribution N2(qc) of excited atoms with the transition moment D forming the angle a against on the transition J =0 the laser intensity I  

Problem 10.3. (a) Molecules with a magnetic moment /x = 0.1 /Xg (/Xg = 9.27-10 2 J/T) pass with v = 500 m/s in the z-direction through an inhomogeneous magnetic field (dB/dx = IT/m, Lg 0.1m) of a Rabi molecular-beam apparatus. Calculate the deflection angle of the molecules with mass m 50 AMU (1 AMU = 1.66 lO kg). 

Problem 10.4. In an optical microwave double resonance experiment the decrease of the population Nj due to excitation into level k) by a CW laser is 20%. The lifetime of the upper level is = 10 s. The collisional refilling rate of level i) is 5 10 s . Compare the magnitude of the microwave signals k) m) between rotational levels 

For some spectroscopic problems it is necessary to use three lasers in order to populate molecular or atomic states that cannot be reached by two-step excitation. One example is the investigation of high-lying vibrational levels in excited electronic states, which give information about the interaction potential between excited atoms at large internuclear separations. This potential V R) may exhibit a barrier or hump, and the molecules in levels above the true dissociation energy V(R = 00) may tunnel through the potential barrier. Such a triple resonance scheme is illustrated in Fig. 5.42a for the Na2 molecule. A dye laser Li excites the selected level (v J ) 

A second example, mentioned already, is microwave spectroscopy of Rydberg levels that have been excited by resonant two-step absorption of two dye lasers (Fig. 10.36b). The high accuracy of microwave spectroscopy allows 

4 In an optical-microwave double-resonance experiment the decrease of 

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Mdbius K, Plato M and Lubitz W 1982 Radicals in solution studied by ENDOR and TRIPLE resonance spectroscopy P/rys. Rep. 87 171-208... 

N,1H]-TROSY - Triple Resonance Spectroscopy for Sequential Assignment 233... 

Bryant, G. P., Yiang, Y., and Grant, E. R. (1992), Triple-Resonance Spectroscopy of the Higher Excited States of N02. Trends in the Mode Dependence of Vibrational Autoionization via Asymmetric Stretch versus Symmetric Stretch and Bend, J. Chem. Phys. 96,4827. 

In collaboration with Fabian Gerson at the University of Basel, the radical anion of 72 was also studied by ESR, ENDOR, and triple-resonance spectroscopy. The results obtained thus far indicated that the odd electron of the radical anion of 72 was delocalized exclusively between the para-linked benzene rings, and was consistent with the result procured from a similar study on the parent [2.2]paracy-clophane. " ... 

Upon treatment of 2,5-dihydro-1,2,3,5-thiatriazole 1-oxides with sodium or potassium (4.20.5.1) in 1,2-dimethoxyethane 2,5-dihydro-l,2,3,5-thiatriazol-5-yl radicals are formed which have been studied by means of ESR, ENDOR, and general triple resonance spectroscopy <90JCS(P2)1619>. 

Dihydro-l, 2,3,5-thiatriazole 1-oxide radicals were generated from the thiatriazole oxides upon hydrogen abstraction in the reaction with thermally formed bis(4-methylphenyl)aminyl (4.20.5.1). Only radicals with aryl substituents in positions two and four are persistent, radicals with alkyl groups in these positions could not be detected. The radicals were investigated by ESR, ENDOR, and general triple resonance spectroscopy <92MRC84>. 

The data on electron spin resonance (ESR), electron-nuclear double resonance (ENDOR), and general triple resonance spectroscopy for 2,5-dihydro-l,2,3,5-thiatriazole-5-yl radicals was reviewed by Holm and Larsen <1996CHEC-II(4)733>. There are no new data on this subject. 

The radical cations from several substituted A V -diphenyl viologens (PV) have also been investigated by means of EPR spectroscopy as well as electron nuclear double resonance (ENDOR) and triple resonance spectroscopies. 

Fig. 5.42 Triple-resonance spectroscopy (a) population of high vibrational levels in the ground state by stimulated emission pumping and absorption of a third laser radiation, resulting in the population of levels just below and above the dissociation energy of the excited A Eu state of Na2 [617] (b) stepwise excitation of Rydberg levels by OODR and microwave-induced transitions to neighboring levels...

Tsai, C.C., Bahns, J.T., and Stwahey, W.C., Observation of Na2 Rydberg states and autoionization resonances by high resolution all-optical triple resonance spectroscopy, Chem. Phys. Lett., 236, 553, 1995. 

Moebius, K., Plato, M., Lubitz, W. Radicals in Solution Studied by ENDOR and Triple Resonance Spectroscopy. Phys. Rep. 87 (1982) 783. 

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