Electronic spectra fluorescence

Figure 3.10 The electronic transitions [absorption in (a)] of small molecules show vibrational and rotational lines in addition to the purely electronic spectrum, (b) Luminescence emission is resonance fluorescence (f), and chemical reactions (R) can originate from several excited states...

The YS molecule has been studied by Azuma and Childs [82], again using the molecular beam laser/radioffequency double resonance technique. The electronic spectrum arising from the /i 2 E 1 Y 2 E 1 transition was studied through fluorescence... 

The ground electronic state of 139La160 is X2S+ audits electronic spectrum involving the excited B2Y,1 has been studied by Doppler-free laser-induced fluorescence by Bacis, Collomb and Bessis [85] and by Bernard and Sibai [86]. Both states have therefore been well characterised and the system is ideal for radiofrequency/optical double resonance, as described by Childs, Goodman, Goodman and Young [87]. They used a collimated molecular beam, with the laser pump/probe technique described elsewhere in this chapter. 

Figure 11.43. Section of the Doppler-free laser-induced fluorescence spectrum of LaO, arising from the B 2E+(u = 0)—> X 2E+ (v = 1) electronic transition [87], Four different rotational components are present, one of which is marked, with the lower state N value (30) being given in the brackets. The region of the electronic spectrum scanned is 5866.75 to 5866.80 A.

The fluorescence spectrum shows a vibrational structure giving the vibrational frequency of the molecule in the ground state. This is in contrast to the electronic state. This follows that the fluorescent spectrum and electronic spectrum should appear as mirror images of each other, but this description should be taken literally. 

Electronic Spectrum. Acetone is the simplest ketone and thus has been one of the most thoroughly studied molecules. The it n absorption spectrum extends from 350 nm and reaches a maximum near 270 nm (125,175). There is some structure observable below 295 nm, but no vibrational and rotational analysis has been possible. The fluorescence emission spectrum starts at about 380 nm and continues to longer wavelengths (149). The overlap between the absorption and the fluorescence spectra is very poor, and the 0-0 band has been estimated to be at - 330 nm (87 kcal/mol). The absorption spectra, emission spectra, and quantum yields of fluorescence of acetone and its symmetrically methylated derivatives in the gas phase havbe been summarized recently (101). The total fluorescence quantum yield from vibrationally relaxed acetone has been measured to be 2.1 x 10 j (105,106), and the measurements for other ketones and aldehydes are based on this fluorescence standard. The phosphorescence quantum yield is -0.019 at 313 nm (105). 

As such, it competes directly with X-ray fluorescence (XRF) but it is not limited by the dipole operator selection rules. All energetically allowed transitions are observed in an Auger electron spectrum. In addition, the electron escape depth is also a few tens of angstroms, unlike XRF where typical escape depths are on the order of tens of thousands of angstroms. 

The fluorescence of the phenyl polymer is similar in shape to the fluorescence from the alkyl polymers and the similar shape of the phosphorescence spectrum, as well, suggests that the origins of the electronic spectrum are also much the same. The apparent increased quantum yield for phosphorescence in poly(phenyl methyl silylene) probably reflects a mixing of the ring electronic levels with the levels of the chain. Both the fluorescence and phosphorescence of the naphthyl derivative are substantially altered relative to the phenyl polymer. Fluorescence resembles that of poly(B Vinyl naphthalene) (17,29) which is attributed to excimer emission. Phosphorescence is similar to naphthalene itself. These observations suggest that the replacement of an alkyl with phenyl moiety does not change the basic nature of the electronic state but may incorporate some ir character. Upon a naphthyl substitution both the fluorescence and phosphorescence become primarily tt-tt like. 

Fluorescence in the visible and ultraviolet regions of the spectrum provides a convenient means for detecting decay produts, both neutral and ionic, produced in excited electronic states. Fluorescence spectra with resolved rotational and vibrational structure provide information about the energy spacing between electronic states, about the structure and bonding properties of these states, and about the populations of rotational and vibrational levels, which can characterize the populating mechanisms associated with decay of the core hole excited state. The production of the doubly charged molecular cation by decay of the core hole is of particular interest because little is known about the properties of these ions and because the fluorescence decay... 

TiIv. Diamagnetic Ti porphyrins have been isolated and characterized as titanyl (Ti =0) complexes [Fuhrhop (71), Tsutsui (181), (183)]. An esr spectrum of a Tim state has been mentioned, but no detailed data are available on this oxidation state nor on the potential of the Ti111/ TiIV couple [Tsutsui (183)]. The "normal electronic spectrum of titanyl OEP [573 (28,000), 535 (14,000) 405 (350,000)] [Fuhrhop (71)] is replaced by a hematin spectrum [582 (8,500) 480 (24,000) 359 (105,000)] [Fuhrhop (71)] and the fluorescence of the original titanyl compound disappears when the axial oxo group is protonated. The influence on the redox potential of the intramolecular n- dxz,yz charge transfer, which occurs similarly in the hematins (see IV.6), has not been investigated. 

The large differences between the S0-Sn absorption spectrum, fluorescence spectrum, and fluorescence decay time of 1,1 -binaphthyl in fluid solutions as compared with those in rigid solutions can be related to a change in the dihedral angle, 6, between the two rings on electronic excitation. The red shift of the fluorescence spectrum demonstrates clearly that after excitation to the Si state,... 

An interesting blue-green pigment, prasinone (370), has been isolated from the green fruit bodies of C. prasinus and other species. It exhibited an absorption maximum at 614 nm in the electronic spectrum and showed purple fluorescence under UV light. From the spectroscopic data, and its co-occurrence with pseudophlegmacin (367), the dibenzo[(2,7]perylenequinone structure (370) has been tentatively proposed 515). 

Figure 3. a) The fluorescence yield spectrum (bulk) is shown for the PBOCSt / PFOS films after different processing, b) The electron yield spectrum (surface) is shown for the same PBOCSt / PFOSfilms. Comparison of the electron and fluorescence yield shows that the surface reaction rate is faster than the bulk. The top illustrates the deprotection reaction of PBOCSt to PHS. 

The UV-vis electronic spectrum exhibited an intense broad absorption which started at a wavelength A < 200 nm and decreased to 460 nm (Figure 9.1). Corresponding to the electronic absorbance, an intensive, broad fluorescence peak with at 460 nm was found in the fluorescence spectrum of the polymer (Figure 9.1). Both UV-vis and fluorescence properties were consistent with the poly(phenylcarbyne) structure [20]. 

Figure 9.1 (a) UV-vis electronic spectrum (cyclohexane) and (b) fluorescence spectrum (cyclohe)ane, excitation wavelength =300 nm) of poly(phenylcarbyne) obtained by this methodology. 

Figure 4.1 Fluorescence spectrum (fluorescence intensity as a function of fluorescence wavelength) for Naa vapor pumped by a 5682-A4 krypton ion laser. This wavelength excites Na2 molecules from v" = 3, J" = 51 in the electronic ground state to v = 34, J = 50 in the excited electronic state. The shown fluorescence lines result from transitions from the laser-excited level down to v" = 4 through 56 in the electronic ground state. Reproduced by permission from K. K. Verma, A. R. Rajaei-Rizi, W. C. Stwalley, and W. T. Zemke, J. Chem. Phys. 78. 3601 (1983).

Schrodinger equation (3.30) can be solved numerically to obtain the corresponding vibrational states y"> and v in the respective electronic states. It is then straightforward to calculate the predicted Franck-Condon factors Kv v" for all vibrational bands in the electronic transition. The band intensities observed in an absorption or fluorescence spectrum should be proportional to these calculated Franck-Condon factors (Section 4.4). If they are not, the vibrational bands in the electronic spectrum may have been incorrectly assigned. In this manner, Zare found it necessafy to reassign the v quantum numbers previously attributed to vibrational bands in the spectrum [13]. RKR... 

Keywords Electronic spectrum Absorption Fluorescence Spectrum simulation Excimer 2-Phenylfuran... 

Raman spectra of many pure colorless compounds can easily be measured with an instrument incorporating a visible laser, scanning double monochromator, and PMT. However, when spectroscopists attempted to measure the corresponding spectra of real-world samples with this type of instrument, good spectra were rarely obtained. The root cause of this difficulty was fluorescence by the sample, either because of its intrinsic electronic spectrum or, more likely, because of low levels of fluorescent impurities. Even for nonfluorescent samples, it often took at least 30 minutes to measure a reasonably noise-free Raman spectrum. Thus, with the exception of a few spectroscopists in industrial labs who could obtain their information in no other way, Raman spectrometry was considered to be largely... 

The colour of the irradiated layer changes from green to brown, which suggests loss of iodine. The % loss in mass was 22.0%. The peaks in the electronic spectrum of a solution in acetonitrile did not rqipear after heating. Under prolonged irradiation, a yellow substance speared at the edges. This substance the original complex and Agl produced, showed fluorescence under uv irradiation. 

Alves, A.C., Hollas, J.M., Musa, M., and Ridley, T. (1985) The 370-nm electronic spectrum of tropolone evidence from single vibronic level fluorescence spectra regarding the assignment of some vibrational fundamentals in the X and A states. J. Mol. Spectrosc., 109, 99. 

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