Rotationally resolved spectra

The rotationally resolved spectra of the doubly hydrogen-bonded complexes (HCOOH)2 and (CH3COOH)2 have been measured for the first time by a spectroscopic technique. Rotational constants and the PT evaluated from the fitting of the fs DFWM spectra are in good agreement with results from ab initio calculations. The values of the CD constants have been obtained from the analysis based on a new general nonrigid asymmetric rotor approach. 

In addition to SO2 self-shielding many other possible sources of S-MIF can be identified. The model A S/results for the case of a I0W-O2 atmosphere (e.g.. Figure 5.7b) are in qualitative but not quantitative agreement with the ancient rock record. Elemental S, derived from S(D, is predicted here to have > 0 and < 0, which is consistent with observations of most pyrites [4], but the magnitude of the A S/A S ratio is about a factor of 2 to 3 too high ( -2.5 vs. 0.9). This is a significant discrepancy, and may indicate that MI processes in addition to SO2 photodissociation are at work. One such MI process almost certain to be important in a I0W-O2 atmosphere is SO photodissociation. Isotope-selective photolysis will occur in SO at wavelengths 190-230 nm, but rotationally-resolved spectra, either laboratory or synthetic, are needed to estimate the MI effect. In addition to S-MIF due to SO photolysis, SO2 photoexcitation ( 280-330 nm) and SO3 photolysis [18] must also be considered as possible contributors to S-MIF in the ancient atmosphere. S-MIF due to these photo-processes will be considered in future work. 

J.M. Hjorthoj, L.A. Philips, Data analysis for rotationally resolved spectra A simulated annealing approach. Journal of Molecular Spectroscopy, 154 (1992) 288.A... 

The Broida oven is a nearly ideal source for the spectroscopy of diatomic molecules and small polyatomic molecules such as CaOH. For larger species, however, the spectral congestion is too severe and the collisional relaxation rates are too high to record resonant, rotationally resolved spectra. The solution to this problem is to lower the temperature to eliminate the spectral congestion and to lower the pressure to eliminate the... 

The spectra in figure 4.16 show that a single atom substitution may have an enormous effect on the intramolecular dynamics, since there is a remarkable difference in the rotationally resolved spectra of the fundamental and first overtone of these two molecules. The line width of the silicon-substituted compound is significantly narrower than that of tert-butylacetylene in both the fundamental and first overtone. There is also a striking different behavior of the two molecules in going from fundamental to overtone excitation. Tert-butylacetylene shows a decreased IVR lifetime in the overtone, dropping by almost a factor of 2. In contrast, the silicon substituted compound shows exactly the opposite behavior since the lifetime in the fundamental is decreased by almost a factor of 2 compared to the overtone. 

High-resolution spectroscopy of cluster ions has largely been limited to binary complexes between a molecular ion and a rare-gas atom or a hydrogen molecule. Much of this work had been done by the group of Maier and Dopfer in Switzerland. The spectrum of Ar-H20" given below in Fig. 17 is an excellent recent example of the rotationally resolved spectra that are possible using a tandem quadrupole mass spectrometer. Except for, Rg2-CH3 where Rg = Ar and larger clusters have yielded... 

With the pair potentials well determined, Ar HF/DF provides a particularly good system for studying the transformation to a more fully solvated complex. Additionally, rotationally resolved spectra for ArnHF/DF (n = 1—4) were already reported in Fourier transform microwave studies by Gutowsky and coworkers, and infrared results have been reported... 

TABLE 1. Rotational excitation of individual vibrational product states. To a good approximation was obtained from a fit of a "rotational temperature" T r(v) to rotationally resolved spectra. 

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