Stark-spectroscopy

Analogous to the LMR technique. Stark spectroscopy utilizes the Stark shift of molecular levels in eleotvio fields to tune molecular absorption lines into resonance with lines of fixed-frequency lasers. A number of small molecules with permanent electric dipole moments and sufficiently large Stark shifts have been investigated, in particular those molecules which have rotational spectra outside spectral regions accessible to conventional microwave spectroscopy [8.35]. 

To achieve large electric fields, the separation of the Stark electrodes is made as small as possible (typically about 1 mm). This generally excludes an intracavity arrangement because the diffraction by this narrow aperture would introduce intolerably large losses. The Stark cell is therefore placed outside the resonator, and for enhanced sensitivity the electric field is modulated while the dc field is tuned. This modulation technique is also common in microwave spectroscopy. The accuracy of 10 for the Stark field measurements allows a precise determination of the absolute value for the electric dipole moment. 

Stark spectroscopy with constant electric fields and tunable lasers has been performed in molecular beams at sub-Doppler resolution to measure the electric dipole moments of polar molecules in excited vibrational states [6.102]. 

An efficient way to generate coherent, tunable radiation in the far infrared is the difference frequency generation by mixing the output of an CO2 laser kept on a selected line with the output of a tunable CO2 waveguide laser in a MIM-diode (Sect.5.8). With this technique Stark spectra of CHsOH were measured over a broad spectral range [6.103]. 

Reviews about more recent investigations in LMR and Stark-spectros-copy, including the visible and UV-range, can be found in [6.104-106]. 

If the laser beam is split into two partial beams which pass into opposite directions through the LMR cell, Doppler-free saturation spectra can be realized (see Sect. 2.2). This allows one to resolve even complex spectra of radicals or neutral molecules. The narrow spectral width of the Lamb-dips facilitates the determination of collisional broadening and the measurement of molecular transition moments. 

1 Doppler-Limited Absorption and Fluorescence Spectroscopy with Lasers 

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Marshaii M D, Charo A, Leung H O and Kiemperer W 1985 Characterization of the iowest-iying n bending state of Ar-HCi by far infrared iaser-Stark spectroscopy and moieouiar beam eiectric resonance J. Chem. Phys. 83 4924-33... 

Figure 9.23 Laser Stark spectroscopy with the sample inside the cavity. G, grating S, Stark electrodes W, window M, mirror D, detector...

Kodali G, Kistler KA, Matsika S, Stanley RJ (2007) 2-aminopurine excited state electronic structure measured by stark spectroscopy. J Phys Chem B 111 10615-10625... 

Okubo et al. have used Stark spectroscopy to study the unusual trinuclear complex salt (76) which has pseudo D3h symmetry and contains tetrahedral Cu1 centers and a symmetrical hexa-azatriphenylene-derived radical anionic ligand.139 The x responses of PMMA thin films doped with (76) are enhanced by an intense, broad MLCT transition which has a maximal absorbance in the NIR region.139... 

In many practical cases, the factors f i are very close to unity and can be omitted. The parameters So, and mo,- are then equal to their gas-phase values oto, and mo,. Equation [100] then gives the polarizability change in terms of spectroscopic moments and gas-phase solute dipoles. Experimental measurement and theoretical calculation of Aao = aoi - ocoi is still challenging. Perhaps the most accurate way to measure Akq presently available is that by Stark spectroscopy,which also gives Awq. Equation [100] can therefore be used as an independent source of Aao, provided all other parameters are available, or as a consistency test for the band shape analysis. 

The differential and transition dipoles can be determined from experiment the former from the Stark spectroscopy and the latter from absorption or emission intensities (see below). 

D. Laughton, S. M. Freund, and T. Oka (private communication) detected for the first time two Ak = 3 forbidden vibration-rotation transitions in the I j band of NH3 using infrared microwave two-photon spectroscopy and laser Stark spectroscopy (cf. Section 4.3). This has made it possible to obtain the Co rotational constant of6.2280 +0.0008 cm"... 

Thus, Eq. 74, with A. yj replaced by the right-hand side of Eq. 83, allows Tp to be specified exclusively in terms of adiabatic observables [30a], that is, A i2 and /z, (obtainable from spectral energy and intensity) and A/( 2 (obtainable from Stark spectroscopy [122, 123]). Of course, these quantities may also be obtained from quantum calculations [30]. In typical applications, Eq. 74 or 83 pertains to a vertical transition for a value of the reaction coordinate (Figure 2a) at the equilibrium position of the initial state (where, in general, i/>, i/>,). It is worth noting, however,... 

An important feature of Eqs. 82 and 94 is that they can in principle be implemented entirely in terms of experimental spectral data. One point requiring special comment is the determination of / da in Eq. 82. While this may be obtained by Eq. 83 if the results of Stark spectroscopy are available, such data are still relatively scarce, thus making it common to use structural data (e.g., r,v/,w or vmi. based on the metal site and the ligand midpoint [120, 135]), as estimated upper limits. In cases where Stark data are at hand, da is often found to be appreciably smaller than .v/.v/ (or /, v//.), especially in cases of strong ML coupling [89, 121-123] (examples are given in Section 1,5,1), Nevertheless, recent analyses based on r,v/,v/ and r.vz. have given numerous examples of reasonable correspondence between and... 

Blinov, L, M., Bamik, M. L, Weyrauch, X, Palto, S. A., Tevosov, A. A., and Haase, W. Photoassisted poling of polymer materials studied by stark spectroscopy (electroabsorption) technique. Chem. Phys. Lett. 231, 246 (1994). 

Barnik, M. L, Blinov, L. M., Weyrauch, T, Palto, S. A., Tevosov, A. A., and Haase, W, Stark spectroscopy as a tool for the characterization of poled polymers for nonlinear optics. In G. A. Lindsay, K. O. Singer, Eds. Polymers for Second-Order Nonlinear Optics, 288 (1995). Natansohn, A., Rochon, R, Gosselin, J., and Xie, S. Azo polymers for reversible optical storage. 1. Poly[4 -[[2-(acryloyloxy)ethyl]ethylamino]-4-nitroazobenzene]. Macromolecules 25,2268 (1992). 

As written in Equation 10.19, Stark spectroscopy is based on the absorption spectrum change (AA) induced by an electric field (of frequency Q). ... 

Excited state properties of molecules are often important parameters in different models of interacting systems and chemical reactions. For example, excited state polarizabilities are key quantities in the description of electrochromic and solva-tochromic shifts [99-103]. In gas phase there has been a series of experiments were excited state polarizabilities have been determined from Laser Stark spectroscopy by Hese and coworkers [104-106]. However, in the experiments most often not all the tensor components can be determined uniquely without extra information from either theory or other experiments. 

B3LYP response calculation in Sadlej s POL basis, this work. Laser Stark spectroscopy, [105]. 

Xi2 = ttansition dipole moment and = CT energy) Laidlaw et al. used a A i2 value calculated for transfer of 1 electron over the geometric Ru -Ru distance to afford j3o = 41 X 10" ° esu [26], whereas Vance et al. obtained jSq = 28 x 10 ° esu by using a A/Xi2 derived from Stark spectroscopy [in 1 1 (v v) ethylene glycol-water at 77 K] [27]. The discrepancy between the latter and that obtained from HRS (81 X 10 ° esu in water) may be due to errors arising from resonance-enhancement in the HRS data [27]. 

Coe, B.J., Harris, J.A., Brunschwig, B.S. Determination of the molecular quadratic non-linear optical responses of V-shaped metallochromophores by using Stark spectroscopy. Dalton Trans. 2384-2386 (2003)... 

Vance, F.W., Hupp, J.T. Probing the symmetry of the nonlinear optic chromophore Ru(trans-4.4 -diethylaminostyryl-2, 2 -bipyridine)3 + insight from polarized hyper-Rayleigh scattering and electroabsorption (Stark) spectroscopy. J. Am. Chem. Soc. 121, 4047-4053 (1999)... 

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