Laser electric resonance spectroscopy

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. 

Pauling L (1960) The nature of the chemical bond, 3rd edn. Cornell Univ Press, Ithaca Liu Y, Guo Y, Lin 1 et al (2001) Measurement of the electric dipole moment of NO by mid-infrared laser magnetic resonance spectroscopy. Mol Phys 99 1457-1461 Coulson CA (1942) The dipole moment of the C-H bond. Trans Faraday Soc 38 433-444 Rayane D, Allouche A-R, Antoine R et al (2003) Electric dipole of metal-benzene sandwiches. Chem Phys Lett 375 506-510... 

In dimers composed of equal molecules the dimer components can replace each other through tunneling. This effect has been discovered by Dyke et al. [1972] as interconversion splitting of rotational levels of (HF)2 in molecular beam electric resonance spectra. This dimer has been studied in many papers by microwave and far infrared tunable difference-frequency laser spectroscopy (see review papers by Truhlar [1990] and by Quack and Suhm [1991]). The dimer consists of two inequivalent HE molecules, the H atom of one of them participating in the hydrogen bond between the fluorine atoms (fig. 60). PES is a function of six variables indicated in this figure. 

In this section we have described in considerable detail just one aspect of the spectroscopy of OH, namely, the measurement of zl-doubling frequencies and their nuclear hyperfine structure. This has led us to develop the theory of the fine and hyperfine levels in zero field as well as a brief discussion of the Stark effect. We should note at this point, however, that OH was the first transient gas phase free radical to be studied by pure microwave spectroscopy [121], We will describe these experiments in chapter 10. We note also that magnetic resonance investigations using microwave or far-infrared laser frequencies have also provided much of the most important and accurate information these studies are described in chapter 9, where we are also able to compare OH with the equally important radical, CH, a species which, until very recently, had not been detected and studied by either electric resonance techniques or pure microwave spectroscopy. 

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... 

Volume 11/19 brings the spectroscopic data on diamagnetic and paramagnetic molecules as well as on molecular ions up to date considering the publications up to and partly including 1990. The spectroscopic information collected in this volume has been obtained principally from gas phase microwave measurements. In addition, gas phase data have been included derived from methods related to microwave spectroscopy by employing a coherent radiation source. These are molecular beam techniques, radio frequency spectroscopy, electron resonance spectroscopy, laser spectroscopy, and double resonance techniques. Some other methods are considered if the accuracy of the derived molecular parameters is comparable to that of micro-wave spectroscopy and no microwave data are available. Examples would be Fourier infirared spectroscopy or electric deflection method. 

The main sources of data are microwave, inlfared and laser induced fluorescence spectroscopy and their related Doppler-free techniques. Results from magnetic and electric resonance methods are also considered. 

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... 

In atomic laser spectroscopy, the laser radiation, which is tuned to a strong dipole transition of the atoms under investigation, penetrates the volume of species evaporated from the sample. The presence of analyte atoms can be measmed by means of the specific interaction between atoms and laser photons, such as by absorption techniques (laser atomic absorption spectrometry, LAAS), by fluorescence detection (laser-induced fluorescence spectroscopy, LIFS), or by means of ionization products (electrons or ions) of the selectively excited analyte atoms after an appropriate ionization process (Figures lA and IB). Ionization can be achieved in different ways (1) by interaction with an additional photon of the exciting laser or of a second laser (resonance ionization spectroscopy, RIS, or resonance ionization mass spectrometry, RIMS, respectively, if combined with a mass detection system) (2) by an electric field applied to the atomization volume (field-ionization laser spectroscopy, FILS) or (3) by collisional ionization by surrounding atoms (laser-enhanced ionization spectroscopy, LEIS). 

Sauer, B.E., Jun Wang, and Hinds, E.A., Laser-rf double resonance spectroscopy of 174 Yhp in the X E" " state Spin-rotation, hyperfme interactions, and the electric dipole moment, 7. Chem Phys., 105, 7412, 1996. 

The technique to shift molecular transitions into coincidence with fixed frequencies of a laser is called laser magnetic resonance (LMR). This type of spectroscopy, which is used for studying unstable molecules, was combined with the double resonance technique by Lowe and McKellar. A radiofrequency double resonance cell was placed in the 6-cm gap of the electromagnet of an intracavity laser magnetic resonance apparatus. The Zeeman magnetic field was oriented parallel to the laser light polarization (AM = 0 infrared transitions) and perpendicular to the electric field vector... 

MB molecular beam electric or magnetic resonance spectroscopy and related methods applying lasers for quantum state preparations... 

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... 

All measurements were made in the gas phase. The methods used are abbreviated as follows. UV ultraviolet (including visible) spectroscopy IR infrared spectroscopy R Raman spectroscopy MW microwave spectroscopy ED electron diffraction NMR nuclear magnetic resonance LMR laser magnetic resonance EPR electron paramagnetic resonance MBE molecular beam electric resonance. If two methods were used jointly for structure determination, they are listed together, as (ED, MW). If the numerical values listed refer to the equilibrium values, they are specified by and 6. In other cases the listed values represent various average values in vibrational states it is frequently the case that they represent the Tj structure derived from several isotopic species for MW or the r structure (i.e., the average internuclear distances at thermal equilibrium) for ED. These internuclear distances for the same atom pair with different definitions may sometimes differ as much... 

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