Laser Stark spectroscopy

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

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"... 

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]. 

Marshall M D, Charo A, Leung H O and Klemperer W 1985 Characterization of the lowest-lying n bending state of Ar-HCI by far infrared laser-Stark spectroscopy and molecular beam electric resonance J. Chem. Phys. 83 4924-33... 

With the sub-Doppler resolution of the Lamb-dip technique, about 500 Stark resonances have been identified for 44 lines of the V2 band and 31 lines of the V4 band [13]. Two Doppler-free lines with signs opposite to those of Lamb dips were observed in a study of the V2 °P(5,3) transition by laser Stark spectroscopy using the 10P(18) CO2 laser line. They were identified as infrared-infrared double resonance transitions, caused by accidental overlapping of the °P(5,3) line in the V2 band with the °P(4,3) line in the hot band 2V2-V2 [14 to 16]. 

This chapter is concerned with the following techniques in molecular laser spectroscopy (i) laser-Stark spectroscopy and electric field spectroscopy (ii) laser-Zeeman, or laser-magnetic-resonance spectroscopy (LMR) (iii) dispersed laser-induced fluorescence and (iv) double resonance spectroscopy. 

Duxbury (1985) has recently published an extensive review of laser Stark spectroscopy. Table 1 lists most of the molecules that have been studied in this way. The majority of these have closed-shell singlet ground states, and their Stark splittings follow eqns 2-5, at least for weak fields. However, one of the more reactive species, HCO, has a doublet ground state. The presence of the unpaired electron spin complicates the energy level pattern, but the same principles hold as for a singlet state. 

Table 1 Molecules studied by laser Stark spectroscopy...

Laser Stark Spectroscopy Laser Magnetic Resonance Laser Induced Fluorescence Double Resonance Spectroscopy... 

Figure 1.50 illustrates the obtainable sensitivity by a AM = 0 Stark spectrum of the ammonia isotope NH2D composed of measurements with several laser lines [146]. An electric resonance signal is observed at every crossing point of the sloped energy levels with a fixed laser frequency. Since the absolute frequency of many laser lines was measured accurately within 20 0 kHz (Sect. 9.7), the absolute frequency of the Stark components at resonance with the laser line can be measured with the same accuracy. The total accuracy in the determination of the molecular parameters is therefore mainly limited by the accuracy of 10 for the electric field measurements. To date numerous molecules have been measured with laser Stark spectroscopy [146-149]. The number of molecules accessible to this technique can be vastly enlarged if tunable lasers in the relevant spectral regions... 

Y. Ueda, K. Shimoda, Infrared laser Stark spectroscopy, in Laser Spectroscopy II, ed. by S. Haroche, J.C. Pebay-Peyroula, TW Hansch. Lecture Notes Phys., vol. 43 (Springer, Berlin, 1975), p. 186... 

Meth. MW MBER Last IRIRDR IRMWDR method of measurement for ft microwave spectroscopy molecular beam electric resonance Laser Stark spectroscopy infrared-infrared double resonance infrared-microwave double resonance... 

The main applications covered in this study are the accurate determination of rotation and rotation-vibration molecular energies the determination of the molecular geometry of simple molecules the evaluation of force field and of the vibration- and rotation-vibration interactions the measurement of pressure broadening and pressure shift of the spectral lines the determination of electric dipole moments via laser-Stark spectroscopy the studies of intramolecular dynamics the calculation of rate constants, equilibrium constants and other thermodynamic data the evaluation of relaxation times. 

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. Figure 8.16 is a block diagram of the experimental setup for laser Stark spectroscopy in the 10 ym region. The accuracy —4... 

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