Molecular beam resonance

Early ab initio HF-LCAO calculations using minimal basis sets were at first thought to have been unsuccessful, in that they gave the polarity C-O", whilst HF-LCAO calculations with extended basis sets gave the polarity C O-. That the polarity is indeed C-O" " was shown by Rosenblum, Nethercott and Townes (1958) from a molecular beam resonance experiment it goes against all chemical inmition. 

Experimentally, x values for gaseous lithium halides were determined as early as 1949 by molecular beam resonance experiments In solution, the quadrupolar interaction of ethyUithium and of t-butyllithium were investigated in 1964 . It was found that tetrameric and hexameric aggregates have different interactions. In the solid state x of tetrameric methyl- and ethyUithium was determined in 1965 and 1966 , and for lithium formate in 1972 . However, it was not untU Jackman started his investigations of lithium enolates and phenoxides in solution that the quadrupolar interaction was used in a systematic fashion to obtain structural information . 

The nuclear quadrupole interaction often produces measurable effects in electronic, rotational, atomic and molecular beam resonance, nuclear magnetic resonance, and MOssbauer spectra. In many cases it can be directly studied by nuclear quadrupole resonance (NQR). The magnitude of interaction is expressed by the nuclear quadrupole coupling constant, e2qQ/hy which is the product of Eq. (1) and (3) expressed as a frequency. 

For small molecules in the gaseous state, quadrupole coupling constants for deuterium and other nuclei can be determined from microwave spectroscopyS4,S6 and molecular beam resonance.43 For systems that behave differently in isolated molecules and in the condensed states, these techniques give unique information. Examples are lithium deuter-ide,61 which has an NaCl structure and therefore a zero field gradient for deuterium in the solid state, and deuterium fluoride,36 which forms strong hydrogen bonds in both the liquid and the solid state. 

Molecular beam resonance can be performed in a magnetic field or an electric field. In molecular beam magnetic resonance, when the Zee-man interaction is much larger than the quadrupole interaction, as it is for deuterium in a high magnetic field, transitions between nuclear spin levels are detected with splittings caused by quadrupole interactions. 

The resulting spectrum represents a weighted average over the rotational states and a careful analysis of it yields the nuclear quadrupole coupling constant. Molecular beam electric resonance is complementary to pure rotational spectroscopy since transitions between the Stark levels of the rotational states (AJ = 0) are observed (sometimes AJ= 1 transitions are also studied). Specially constructed maser spectrometers55 that can detect transitions of rotationally selected molecules have been used to determine very small coupling constants, such as those for deuterium compounds. Again, molecular beam resonance is currently limited to the study of small molecules. 

Molecular beam resonance experiments performed on CsBr and LiBr resulted in a coarse determination of the Br nuclear magnetic moments. Pound subsequently used solution-state Br NMR experiments (a negative solid-state experiment was attempted on a single crystal of KBr) to improve the precision of both magnetic moments by nearly an order of magnitude. The first bromine SSNMR spectrum ( Br) was acquired by Pound using a single crystal of NaBr. Relative to far fewer liferature reporfs confain Br SSNMR experi-... 

S.D. Rosner, R.A. Holt, T.D. GaUy, Measurement of the zero-field hyperfine structure of a single vibration-rotation level of Na2 by a laser-fluorescence molecular-beam resonance. Phys. Rev. Lett. 35, 785 (1975)... 

A.G. Adam, Laser-fluorescence molecular-beam-resonance studies of Na2 lineshape due to HFS. PhD thesis, Univ. of Western Onttirio, London, Ontario, 1981 ... 

Rabi, I.I. MiUman, S., Kusch, R, and Zacharias, J.R., The molecular beam resonance method for measuring nuclear magnetic moments, Phys. Rev., 55, 526-535, 1939. 

N.F. Ramsey A new molecular beam resonance method. Phys. Rev. 76, 996 (1949) A molecular beam resonance method with separated oscillating fields. Phys. Rev. 78, 695 (1950) Phase shifts in the molecular beam method of separated oscillating fields. Phys. Rev. 84, 506 (1951)... 

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)... 

State distributions for some simple diatomic product molecules could be measured by using the molecular beam resonance method (27,28) or laser-induced fluorescence (29,30) ... 

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... 

Ramsey, N. F. (1950). A molecular beam resonance method with separated oscillating fields. Physical Review, 78, 699-703. 

---