Bending-Mode Vibrational Structure

The variation of the excited-state vibrational intervals AG(v2+1/2) of PH2 and PD2 [12] with increasing transition energy V2 Tq(V2) + To(V2+1), is shown in Fig. 6 taken from [29, 30]. The minimum of AG(v2+l/2) has been called a Dixon dip [30] and occurs approximately at the barrier to linearity of the potential energy curve [29]. The Dixon dip thus is one consequence of the quasi-linear behavior of the radical. Another consequence is the need to introduce the rotational quantum number K (or Kg) into the vibrational analysis. K describes the rotational angular momentum about the inertial a axis, which becomes the molecular axis In the linear 

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The Raman spectra of WO3, 25-NiO-TiO2/30-WO3, 25-Ni0-Ti02/15-W03, 25- NiO-Ti02/5-W03, and Ti02 under ambient conditions are presented in Fig. 1. The WO3 structure is made up distorted WO3 octahedra. The major vibrational modes of WO3 are located at 808, 714, and 276 cm, and have been assigned to the W=0 stretching mode, the W=0 bending mode, and the W-O-W deformation mode, respectively [7]. The Raman spectrum of the 25-... 

Chapter 3 is devoted to dipole dispersion laws for collective excitations on various planar lattices. For several orientationally inequivalent molecules in the unit cell of a two-dimensional lattice, a corresponding number of colective excitation bands arise and hence Davydov-split spectral lines are observed. Constructing the theory for these phenomena, we exemplify it by simple chain-like orientational structures on planar lattices and by the system CO2/NaCl(100). The latter is characterized by Davydov-split asymmetric stretching vibrations and two bending modes. An analytical theoretical analysis of vibrational frequencies and integrated absorptions for six spectral lines observed in the spectrum of this system provides an excellent agreement between calculated and measured data. 

A progression of up to four components in this mode can be observed, the second component being usually the most intense. The information obtained thus on the vibrational structure of the first transition can be applied also to those molecules in which the vibrational structure of this transition cannot be resolved. This situation is the result of the excitation of lower frequency quanta (probably skeletal out of plane bending modes) in combination with the stretching mode. In sterically hindered molecules which show such resolved spectra, the excitation of these low frequency modes would be less probable because of their steeper potential curve. 

In a smaller molecule (HCP), these diagnostically important changes in vibrational resonance structure are manifest in several ways (i) the onset of rapid changes in molecular constants, especially B values and second-order vibrational fine-structure parameters associated with a doubly degenerate bending mode (ii) the abrupt onset of anharmonic and Coriolis spectroscopic perturbations and (iii) the breakup of a persistent polyad structure 15]. 

Direct ionization produces a staircaselike structure in the plot of ion current as a function of photon energy, where the height of each step is proportional to the probability of production of a certain vibronic state of the ion. Such favorable cases of staircaselike structure have been observed for ammonia87 and acetylene.88 The structure in ammonia is attributable to excitation of successive vibrational levels of the out-of-plane bending mode of the ion and in acetylene, to excitation of the C-C stretching mode. As a result, these molecules are favorable candidates for studying the effects of vibrational excitation on the cross sections for ion-molecule reactions. 

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