General expressions are derived for calculating Franck—Condon factors for most transitions of polyatomic molecules (excluding transitions between linear and bent configurations) in the harmonic oscillator approximation. The derivation employs the method of generating functions and also linear transformation of normal mode coordinates between initial and final states. Input data required in the general case are geometries, frequencies, and vibrational force fields for the initial and final states. Explicit algebraic expressions are presented for the transition between linear, symmetric, triatomic initial and final states. The results are used to show that fragmentation cannot result from direct vertical ionization to the ground electronic states of CS2+ and CO2+ or to the excited 2IIu state of CO2+. An attempt was made to fit the experimental photoionization data for C2H2 and C2D2. This resulted in an estimated increase of 0.05 Å in the equilibrium C–C bond distance and no change in the C–H bond distance in C2H2+ as compared to C2H2.
A large isotope effect has been experimentally observed in dissociative attachment of electrons (H 2 +e -H+H"") 1 * 2 in H 2 , HD, and D 2 . The cross section for production of H~ from H 2 exceeds the sum of the cross sections for H~ and D~" from HD, which in turns exceeds that for D~~ from D 2 .The apparatus, a total-ionization tube similar to the device of Tate and Smith, 3 has been described previously. 4 The electron beam was obtained from an indirectly heated oxide-coated cathode and collimated by an axial magnetic field of 500 gauss. Complete collection of all the ions formed in a fixed path length of the electron beam was achieved by increasing the ion draw-out field until there was no further increase in current to the ion collector plate. Typical saturation curves for the negative ions are shown in Fig. 1, in which Fy is the ion draw-out field in V/cm. It is found that the H~ ions produced in H 2 may be described in terms of two different categories according to their kinetic energy. 2 The H~ ions produced by electrons between about 8 and 12.5 eV have -3^.5 eV of initial kinetic energy, whereas the H ions produced near 14.0 eV have almost no initial kinetic energy. It is apparent that a higher ion draw-out field is required for complete collection of the energetic H~ ions. The saturation is not completely flat at high V,.for 14-eV electrons because the energy spread introduced by the ion draw-out field (-±0.05 eV per 10-V/cm field) reduces the apparent cross section due to the sharp resonance energy dependence of the cross section. It was found that by using an ion draw-out field of 24 V/cm between 7 and -12.8 eV, and 10 V/cm above -12.8 eV, nearly complete collection could be achieved over the entire energy range. At about 12.8 eV, the ion current was essentially the same for either field. A discussion of other consistency checks is given in reference 4. The energy spread of the electron beam used in taking the data shown in Fig. 2 was 0.30 eV full width at half-height. 5 However, in a single run taken in H 2 with an electron energy distribution width of 0.15 eV, the cross section was essentially the same. Since the electron current had a smaller absolute value with the narrower distribution, the weaker ion currents were somewhat more noisy, and the results are not presented here. 5 The absolute energy scale was established in two ways. The linearly extrapolated onset of positive ions was found to be 15.4 eV 4 ' 6 by comparison with positive ions in He, Ne, and Ar in the "total-collection mass-spectrometer" version of the total-ionization tube. Reversal of the ion draw-out field and study of the positive ions establishes the energy scale. Alter-533
Dissociative electron attachment study to nitromethaneCross sections for total negative ions and amino negative ions have been measured as a function of energy for dissociative attachment of electrons in the gases NHa and NDa. Two peaks are observed, at 5.?5 and 1?5 eV. Both peaks contain H-(D-) and NH2-(ND2-). Small direct isotope effects were found, In negative ion production, except for H-/Dformation at 5.65 eV where the isotope effect was 1.0~ The peak at ~.65 eV leads to products in their ground states. The corresponding potential-energy-v~-Internuclear-distance (H-NH2) curve for NHa -may contain a hump or may merely have a shallow sl~pe In the Fra,:ck-Cond~n region. The peak at 10.5 eV arises from a repulsive state of NHa-, and the a~no fragment IS ~orm~d In an excited state. Empirical trends in the isoelectronic series methane, ammoma, and water are Identified.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.