Fluorescence dip spectroscopy

This section will focus on the stmcture and energetics of chiral molecular complexes studied with Fourier-transform IR (FT-IR), microwave, LIF, hole burning (HB), IR fluorescence dip spectroscopy, resonance-enhanced multiphoton ionization (REMPl Fig. 5), and RET spectroscopy. 

Figure 29.1 (a) Scheme of two-color fluorescence dip spectroscopy. The pump beam excites a molecule from the ground state (S0) to the S i state. Then, the erase beam further excites the St molecule to a higher excited state, S . Due to various relaxation processes from S states, such as internal conversion to the ground state,... 

Watanabe, T., Iketaki, Y., Omatsu, T., Yamamoto, K. and Fujii, M. (2005) Two-point separation in far-field superresolution fluorescence microscopy based on two-color fluorescence dip spectroscopy, Part I Experimental evaluation. Appl. Spectrosc., 59, 868-872. 

Fig. 5.40 Fluorescence-dip spectroscopy of C6H6 molecules. The upper rotational level J = 6, = 6, f — 1 of the 6 V vibrational state has been selectively excited by L2 and the fluorescence...

Structure. As for ground state IR-UV ion dip spectroscopy, the depletion in the electronically excited state caused by IR absorption can also be probed via LIF. LIF detection should be equally applicable to ground state and excited states, but has more limited application as strongly fluorescent molecules are required [102, 104, 105]. 

Walther T, Bitto H, Minton TK, Huber JR (1994) UV-IR double-resonance spectroscopy of jet-cooled propynal detected by the fluorescence dip method. Chem Phys Lett 231(l) 64-69... 

Seurre N, Le Barbu-Debus K, Lahmani F, Zehnacker-Rentien A, Sepiol J (2003) Electronic and vibrational spectroscopy of jet-cooled m-cyanophenol and its dimer las -indnced fluorescence and fluorescence-dip IR spectra in the So and Si states. Chem Phys 295 21... 

Figure 12-1. Schematic diagram to illustrate double resonance techniques, (a) REMPI 2 photon ionization. The REMPI wavelength is scanned, while a specific ion mass is monitored to obtain a mass dependent SI <- SO excitation spectrum, (b) UV-UV double resonance. One UV laser is scanned and serves as a burn laser, while a second REMPI pulse is fired with a delay of about 100 ns and serves as a probe . The probe wavelength is fixed at the resonance of specific isomer. When the burn laser is tuned to a resonance of the same isomer it depletes the ground state which is recorded as a decrease (or ion dip) in the ion signal from the probe laser, (c) IR-UV double resonance spectroscopy, in which the burn laser is an IR laser. The ion-dip spectrum reflects the ground state IR transitions of the specific isomer that is probed by the REMPI laser, (d) Double resonance spectroscopy can also use laser induced fluorescence as the probe, however that arrangement lacks the mass selection afforded by the REMPI probe...

The conformational landscape of phenylalanine (R=CH2-C6Hs, m.p. = 270-275°C) has been widely investigated [11, 137-147]. Six conformational species were identified using laser induced fluorescence LIF, hole burning UV-UV, and ion dip IR-UV spectroscopy coupled with ab initio calculations [11, 137-141]. Lee et al. [141] carried out a definitive identification of the conformers of phenylalanine, based upon comparisons between the partially resolved ultraviolet band contours and that simulated by ab initio computations. The study of the rotational spectrum of phenylalanine by LA-MB-FTMW [153] showed rather weak spectra of only two conformers, Ila and Ilb (see Fig. 21). Both conformers exhibit a trans configuration in the COOH group, being stabilized by O-H- N and N-H- - -it... 

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