Submillimeter Wave Spectroscopy

Soon after the first successful experimental verification of an optical maser the search for possible new laser media began and, especially in the infrared region, numerous stimulated transitions were discovered many of them had not even been observed previously in spontaneous emission 

Most of the infrared laser lines originating from transitions between vibrational-rotational levels in different electronic states of diatomic molecules, e. g. N2, Oj, H, D2, CO, CN, etc., have been meanwhile correctly indentified Some lines and term systems have been found which had never been observed before 354a) 

It is more difficult to assign lines in laser systems which use polyatomic molecules in pulsed gas discharges 355) since here it is not always easy to decide whether the observed lines belong to transitions of the parent molecule or of dissociation products. 

Several investigations concerned with the identification of these lines succeeded, for instance, in the case of H2O, in elucidating the rotational spectrum in excited vibrational states 356). Through comparison of wavelengths and intensities of many lines in H2O , H2 0 and DjO isotopic effects could be studied in these excited vibrational levels 357,358) Perturbations of rotational levels by Coriolis resonance which mixes different levels could be cleared up through the assignment and wavelength measurement of some DCN and HCN laser lines 359). 

Bridges and Chang 360) obtained very accurate rotational constants of CO2 from measurements of beat frequencies between CO2 vibrational-rotational laser lines. They mixed the frequencies from 37 pairs of cw laser lines, each stabilized to line center, in a bulk 

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Much has been learned in recent years about the 00 dimer , O2O2, produced in reaction 17. It is actually dichlorine peroxide, OOOCl its geometry is now well established from submillimeter wave spectroscopy (15). Photolysis of OOOO around 310 nm the atmospherically important wavelengths -- yields chlorine atoms and ClOO radicals (16), as given in reaction 18, rather than two OO radicals, even though QO-OQ is the weakest bond (it has a strength of about 17 Kcal/mol (17)). Thermal decomposition of QOOQ (the reverse of reaction 17) occurs very fast at room temperature, but more slowly at polar stratospheric temperatures. Hence, photolysis is the predominant destruction path for CIOOQ in the polar stratosphere and two Q atoms are produced for each ultraviolet photon absorbed. 

By using a combination of gas-phase synthesis and millimeter/submillimeter-wave spectroscopy, LiNH2 was found to be a monomeric unsolvated planar molecule. The lithium amide [H2NCH2CH2N(H)Li]co has a polymeric ladder structure with two types of (NLi)2 ring which alternate throughout its infinite length. ... 

OlMae Maeda, A., Hirao, T., Bemath, P.F., Amano, T. Submillimeter-wave spectroscopy of TiCl in the ground electronic state, J. Mol. Spectrosc. 66 (2001) 250-258. 

Nuss M C and Orenstein J 1998 Terahertz time domain spectroscopy Millimeter Submillimeter Wave Spectrosc. Solids 74 7-50... 

Figure 1 The J = 34 <— 33 transitions of trioxane [(H2CO)3] at 358 GHz. The K=3n transitions are easy to recognize and their quantum number K s indicated. Reproduced with permission from Gadhi J, Wlodarczak G, Boucher D and Demaison J (1989) The submillimeter-wave spectrum of trioxane. Journal of Molecular Spectroscopy 33 406.

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