We report a new mechanism for intramolecular vibrational redistribution (IVR) in CF3CHFI which couples the CH chromophore vibrations through a strong Fermi resonance to the formal CF stretching normal mode (a heavy atom frame mode) involving the trans F-atom across the CC bond. The analysis is made possible by comparing spectroscopic results with extensive ab initio calculations of the vibrational fundamental and overtone spectra in the range extending to 12 000 cm−1. Potential energy and electric dipole moment hypersurfaces are calculated ab initio by second order Møller–Plesset perturbation theory (MP2) on a grid involving the CH stretching, two CH bending modes and one high frequency CF stretching normal mode. The potentials are scaled to obtain agreement between the experimental spectrum and the theoretical spectrum calculated by a discrete variable representation technique on this grid. Both spectra are then analyzed in terms of three-dimensional (3D) and four-dimensional (4D) effective vibrational Hamiltonians including Fermi- and Darling–Dennison-type resonances between the CH stretching mode and the CH bending modes and the CF stretching mode. The interaction between the CH modes and the CF mode is clearly visible in the experimental and calculated (4D) spectra. The effective Fermi resonance coupling constants [ksff′≃(40±10) cm−1 and ksaf′≃(55±10) cm−1] coupling the CH and CF mode subspaces are of about the same magnitude as the intra-CH chromophore Fermi resonances (ksaa′≃56 cm−1 and ksbb′≃42 cm−1, coupling CH stretching mode “s” with the two CH bending modes “a” and “b”). The chiral, pseudo-Cs symmetry breaking coupling (ksab′≃11 cm−1) is complemented by an equally strong coupling through the CF mode (ksfb′≃15 cm−1). It is demonstrated that low order perturbation theoretical analysis using potential constants from a polynomial expansion to represent effective coupling constants gives inadequate results with discrepancies ranging about from factors of 2–5. Time dependent population and wave packet analysis shows essentially complete IVR among the CH chromophore modes within about 100 fs, the 3D and 4D evolutions being similar up to about that time. At longer times of about 250 fs, there is substantial excitation of the CF stretching mode (with initial pure CH stretching excitation). The 4D treatment is then essential for a correct description of the dynamics.

COMMUNICATIONSwith a normal focus molybdenum-target X-ray tube operated at 2.0 kW (50 kV. 40 mA) 191. A total of 1321 frames ofdata were collected using a narrow-frame method with scan widths of 0.3' in w and exposure times of 30 sec per frame using a crystal-to-detector distance of 6.015 cm (maximum 211 angle 51.62"). The total data collection time was approximately 13 h. Frames were integrated with the Siemens SAINT program to yield a total of 14059 reflections, of which 2213 were independent (R,,, = 0.0307, Laue symmetry hlmmm, R,,, = 0.01 79) and 1993 were above 4u(F). The unit cell parameters (at 153 K) of u = h = 16.5617(2), c = 15.4433(2) A were based upon least-squares refinement of the three-dimensional centroids of 8192 reflections. The cell volume and density were 3668 A' and 1.547 gcm-3, respectwely. By assuming a merohedrally twinned trigonal specimen, twinning law (0 -1 0 -1 0 0 0 0 -1) and space group P%l, Ru of position A is found at (1/3,2/3. z) (site simmetry C35)

Previous experimental and theoretical results on the strength of the important fine structure transition in the Iodine atom scatter over a very wide range, indicating great uncertainty. We have therefore carried out new theoretical calculations and experiments to reinvestigate the transition probability between the fine structure levels 2P3/2 and 2P1/2 in the electronic ground configuration of atomic iodine. In the experiments a tunable, narrow band width, near‐IR laser was used to measure the iodine absorption spectrum with sub‐Doppler resolution. The I‐atoms in the 2P3/2 ground state are produced either in a I2 = 2I equilibriums at elevated temperatures or from IR‐multiphoton dissociation of CF3I, CF3CHFI or C6F5I. The two different experimental methods to produce I‐atoms in the ground state allow for a careful check on possible systematic errors. In the experiments an integrated absorption cross section of Gexp = ∫ σ(v) dln v = (1050±250) fm2 was determined, corresponding to a radiative lifetime of 140 ms for spontaneous emission from the upper level. We have in addition carried out nonrelativistic MCHF calculations and relativistic Dirac‐Fock calculations on this transition. The results of the MCHF calculations (1200 fm2) agree well with experiment and a crude estimate from a simple LS coupling model.

We report results of ab initio calculations on the main features of the potential energy hypersurface of fluorooxirane H 2 COCHF near the equilibrium geometry and for several possible reaction pathways in thermal, chemical activation, and infrared laser chemical experiments. The ab initio results are compared to recent spectroscopic and kinetic data for this compound. The laser chemical reaction dynamics during and after infrared multiphoton excitation is simulated in detail ab initio and with adjustment of some of the potential parameters to reproduce the experimentally dominant channels leading to ketene and HF (or DF) for various isotopomers.

ZUSCHRIFTEN hoherer Frequenz auf. Zum Beispiel ist eine der regelmaoigsten V0,-Oktaederstrukturen im Decavanadat in Na, VloO,, . 18 H,O enthalten; der hochste Wert fur die Frequenz der Streckschwingungsbande dieser Struktur betragt 830 cm-.Is1 Wir ordnen die AM-6-Bande bei 870 cm-relativ ungestorten V0,-Oktaedern zu. Da die Raman-Spektren die fur V,O, charakteristischen Banden bei 994, 701, 526 und 481 cm-' nicht zeigen, scheinen unsere AM-6-Proben kein V,O, zu enthalten. Die Struktur von AM-6 kann nur (kurze) terminale V=O-Bindungen an Defekten oder an der Oberfliche der Kristallite enthalten. Damit iibereinstimmend erscheint die Hauptbande von AM-6 bei 870 cm-', die mit V=O-Bindungen assoziierten Raman-Banden erscheinen gewohnlich bei 900-1000 cm-'.I8] Bei genauer Betrachtung des Spektrums von AM-6 ist eine schwache Bande bei 946 cm-' zu sehen (die bei ETS-10 nicht auftritt), die vielleicht auf eine relativ geringe Zahl an V=O-Bindungen in den zuvor erwahnten Umgebungen zuriickzufiihren ist. Die meisten Banden von AM-6 im Spektralbereich 100 bis 700 cm-' sind auch im Spektrum von ETS-I0 enthalten. Die Banden des ersteren sind jedoch sehr vie1 schwacher und scheinen bei geringfiigig anderen Frequenzen zu erscheinen. Die Bande bei 461 cm-' ist im Spektrum von ETS-10 nicht zu sehen.Das Raumtemperatur-ESR-Spektrum von AM-6 (nicht dargestellt) zeigt ein einzelnes und relativ breites Resonanzsignal (Breite von Peak zu Peak ca. 53 G), zentriert bei g = 1.9545, ohne Hyperfeinstruktur, das die Anwesenheit von (nicht isolierten) V4+-Ionen anzeigt, die in dipolarer Wechselwirkung rnit anderen V4+-Ionen stehen. Obwohl wir nicht in der Lage waren,