Evolution of Microwave Spectroscpy at the National Bureau of Standards (NBS) and the National Institute of Standards and Technology (NIST) (original) (raw)

Advances and Applications of Microwave Spectroscopy

Chinese Journal of Analytical Chemistry, 2008

Advances and applications of microwave spectroscopy are recommended, and the instrument structure and principle are also illuminated. Its applications in the analyses of molecular structure, conformation, weakly bound complexes, analytical chemistry, and interstellar media are reviewed. Future trends of microwave spectroscopy are discussed.

Microwave Spectroscopy of Astrophysical Molecules

Highlights of Astronomy, 1989

Recent detections of new molecules in dense interstellar clouds, first detections of certain chemical elements in interstellar molecules, and new information on isotopic fractionation of hydrogen in the interstellar medium are discussed in the context of the need for new laboratory data on transition rest frequencies, reaction rates, and branching ratios.

Pulsed nozzle Fourier transform microwave spectrometer: Ideal to define hydrogen bond radius

2000

A pulsed nozzle Fourier transform microwave (PNFTMW) spectrometer has been recently fabri- cated at the Indian Institute of Science. The basic design is the same as that of Balle and Flygare. How - ever, recent advances in microwave and computer technologies have helped in designing a state -of-the- art PNFTMW spectrometer. The range of the spectro- meter is from 2

The microwave spectroscopy study of 1,2-dimethoxyethane

Journal of Molecular Spectroscopy, 2017

The pure rotational spectrum of 1,2-dimethoxyethane was measured in the 6-18 and 59.6-74.4 GHz frequency ranges using a cavity-based pulsed jet Fourier transform microwave spectrometer and a Stark modulated free-jet millimeter-wave absorption spectrometer, respectively. Two conformers, TGT and TGG 0 , have been identified, together with their mono-substituted 13 C isotopologues. Each rotational transition is split into several components due to the two methyl groups internal rotations. The corresponding V 3 barriers have been experimentally determined. MP2/6-311++G(d,p) calculations have provided the determination of the conformational stabilities, structures and spectroscopic parameters.

The hydrogen bond: a molecular beam microwave spectroscopist’s view with a universal appeal

Physical Chemistry Chemical Physics, 2009

In this manuscript, we propose a criterion for a weakly bound complex formed in a supersonic beam to be characterized as a 'hydrogen bonded complex'. For a 'hydrogen bonded complex', the zero point energy along any large amplitude vibrational coordinate that destroys the orientational preference for the hydrogen bond should be significantly below the barrier along that coordinate so that there is at least one bound level. These are vibrational modes that do not lead to the breakdown of the complex as a whole. If the zero point level is higher than the barrier, the 'hydrogen bond' would not be able to stabilize the orientation which favors it and it is no longer sensible to characterize a complex as hydrogen bonded. Four complexes, Ar 2-H 2 O, Ar 2-H 2 S, C 2 H 4-H 2 O and C 2 H 4-H 2 S, were chosen for investigations. Zero point energies and barriers for large amplitude motions were calculated at a reasonable level of calculation, MP2(full)/aug-cc-pVTZ, for all these complexes. Atoms in molecules (AIM) theoretical analyses of these complexes were carried out as well. All these complexes would be considered hydrogen bonded according to the AIM theoretical criteria suggested by Koch and Popelier for C-HÁ Á ÁO hydrogen bonds (U. Koch and P. L. A. Popelier, J. Phys. Chem., 1995, 99, 9747), which has been widely and, at times, incorrectly used for all types of contacts involving H. It is shown that, according to the criterion proposed here, the Ar 2-H 2 O/H 2 S complexes are not hydrogen bonded even at zero kelvin and C 2 H 4-H 2 O/H 2 S complexes are. This analysis can naturally be extended to all temperatures. It can explain the recent experimental observations on crystal structures of H 2 S at various conditions and the crossed beam scattering studies on rare gases with H 2 O and H 2 S.