Spectroscopy molecular beam magnetic resonance

Molecular nitrogen, N2, is one of the most extensively studied diatomic molecules and optical spectroscopy has provided a wealth of information about its ground and excited electronic states. Molecular beam magnetic resonance studies of N2 in its ground state have yielded information about 14N nuclear spin dipolar and quadrupole interactions. Similar studies of N2 in its electronically excited A 3LU state were described in two very extensive papers by Freund, Miller, De Santis and Lurio [43] (paper I) and De Santis, Lurio, Miller and Freund [44] (paper II). We will describe their results and analysis in detail, but first note in passing that, strictly speaking, the lowest excited triplet state should be labelled the a state the label A has been used by all concerned in the past, so we will continue to do so. 

The origins and history of Spectroscopy with coherent radiation is reviewed from the earliest molecular beam magnetic resonance experiments up to the development of the laser. 

Various spectroscopic techniques of atomic, molecular and solid-state physics are employed in order to obtain experimental NQCC values such as atomic and molecular beam magnetic resonance, optical and rotational spectroscopy, nuclear quadrupol resonance (NQR) in solids or nuclear magnetic resonance (NMR). Atoms containing /u or tt mesons... 

The years from 1960 to 1975 represented a golden era in the radiofrequency and microwave spectroscopy of open shell diatomic molecules. Molecular beam electric resonance was one of the most important experimental approaches, but microwave, far-infrared and magnetic resonance studies of bulk gaseous samples were equally important and our understanding of these open shell species is derived from a combination of different experimental approaches. In this book we have chosen to organise our descriptions according to the experimental techniques employed, but as with any such scheme, we run the risk, which we wish to avoid, of not connecting the results from different types of experiment in a coherent manner. As we shall see, the OH radical is the example par excellence which illustrates the pitfalls of an approach which is technique-oriented, rather than molecule-oriented. 

We have already discussed the high-resolution spectroscopy of the OH radical at some length. It occupies a special place in the history of the subject, being the first short-lived free radical to be detected and studied in the laboratory by microwave spectroscopy. The details of the experiment by Dousmanis, Sanders and Townes [4] were described in section 10.1. It was also the first interstellar molecule to be detected by radio-astronomy. In chapter 8 we described the molecular beam electric resonance studies of yl-doubling transitions in the lowest rotational levels, and in chapter 9 we gave a comprehensive discussion of the microwave and far-infrared magnetic resonance spectra of OH. Our quantitative analysis of the magnetic resonance spectra made use of the results of pure field-free microwave studies of the rotational transitions, which we now describe. 

W.L. Meerts, F.H. De Leeuw, A. Dymanus, Electric and magnetic properties of carbon monoxide by molecular-beam electric-resonance spectroscopy. Chem. Phys. 22(2), 319-324 (1977)... 

Meth. MW MB IR MODR method of measurement used in the given reference corresponding to the preceding quoted values microwave spectroscopy molecular beam resonance experiment-electric or magnetic resonance infrared with lasers microwave optical double resonance... 

Meth. LC QB OS ED MW MB EPR DR method of measurement for the values in this line of the table level crossing spectroscopy quantum beat spectroscopy optical spectroscopy electric deflection method microwave spectroscopy molecular beam resonance experiment-electric or magnetic resonance electron paramagnetic resonance double resonance experiments (MODR, RF/DR)... 

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... 

Meth. DR LA LM MB MW RA method of measurement applied to obtain the reported value double resonance experiments (microwave-optical double resonance MODR or radiofrequency-optical double resonance RFDR) Doppler free laser spectrosefipy laser magnetic resonance molecular beam electric resonance or molecular beam resonance with laser detection method microwave spectroscopy radio astronomy... 

All of these quantities can (in principle) be obtained in the gas phase or in molecular beams with high-resolution microwave spectroscopy and molecular beam magnetic or electric resonance. Such data provide isolated molecule values (usually selected as to vibrational and rotational state) with which to compare liquid crystal and solid state values. These techniques reveal the desired tensor components by their relationship to the principal inertial axes of the molecule. 

Methods-. Another method of establishing an absolute shielding scale is by using the relationship [equation (8)] between a and the spin-rotation constant measured in a molecular beam magnetic or electric resonance experiment or by high-resolution microwave spectroscopy. Combined with an accurate calculation of in the molecule, the absolute shielding of a suitable primary reference molecule can be obtained. For C and "O the primary reference molecule is CO for P it is PH3. The spin-rotation constant may also be obtained from the ratio of the relaxation times of two nuclei in the same molecule in the gas phase when both are wholly relaxed by the spin-rotation mechanism. In SeF, for example... 

Table 2. Absolute Shielding Scales Based on Measured Spin-Rotation Constants (Method 3 in the Text) from Molecular Beam Magnetic/Electric Resonance or High-Resolution Microwave Spectroscopy...

---