In this manuscript the available experimental and theoretical information on (NO)2 and its ions is summarized and reviewed, and high resolution two photon, one color photoelectron spectra of the dimer are presented. The new spectra yield a wealth of information about the dimer cation, including possibly all six of its vibrational frequencies as well as several anharmonic intermode constants. The most consistent interpretation of the contradictory data available in the literature and of the present results is to assign the gas phase photoelectron spectrum to cis–cis ionization, and the matrix spectra to the trans (NO)2+ ionic ground state. The similarity between the observed matrix frequencies with the gas phase values reflects the insensitivity of the NO stretching fundamentals of the dimer cation to conformation, a point of view supported by the results of theoretical calculations. Despite the problems of theory in computing properties of the (NO)2 species, the experimental structures and molecular constants appear to be in an acceptable agreement with the most recent computational results.

Nachrichten aus Chemie, Technik und LaboratoriumVolume 44, Issue 7-8 p. 807-807 Bücher Spektroskopie-Lehrbuch: Spectra of Atoms und Molecules. Von P. F. Bernath. Oxford University Press, Oxford, 1995. 400 5., geb., 49,95 £. ISBN 0-19-507598-6. Klaus Müller-Dethlefs, Klaus Müller-Dethlefs GarchingSearch for more papers by this authorAndreas Strobel, Andreas Strobel YorkSearch for more papers by this author Klaus Müller-Dethlefs, Klaus Müller-Dethlefs GarchingSearch for more papers by this authorAndreas Strobel, Andreas Strobel YorkSearch for more papers by this author First published: Juli 1996 https://doi.org/10.1002/nadc.19960440730AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume44, Issue7-8Juli 1996Pages 807-807 RelatedInformation

Both spin–orbit states of C2H5I+, the X̃1 2E1/2 and the X̃2 2E1/2 electronic states, are studied by one-color two-photon ionization of ethyl iodide, utilizing the zero kinetic energy pulsed field ionization (ZEKE-PFI) photoelectron technique. Compared with conventional photoelectron data the two-photon spectra exhibit a more extensive vibrational structure mainly involving the C–I stretching and the C–C–I bending modes. This additional vibrational excitation in the two-photon spectra is discussed in terms of mode selective resonance enhancement by the dissociative Ã-state continuum. Accurate values for the vibrational frequencies and the ionization energies are obtained. The appearance of nontotally symmetric modes in the two-color ZEKE spectra is reported.

During the past decade zero kinetic energy photoelectron spectroscopy (ZEKE-PES)1 has become one of the most important techniques for gas-phase studies of molecular ions and ionic complexes. Compared to conventional photoelectron techniques a resolution enhancement by 2 to 3 orders has been achieved and even the rotational structure of larger polyatomic ions can be resolved.2

We have reinvestigated the NO dimer cation, (NO)(2)(+), both in the gas phase by high-resolution zero kinetic energy-pulsed field ionization (ZEKE-PFl) photoelectron spectroscopy and by infrared absorption spectroscopy in a solid neon matrix. Comparison of the results leads to the conclusion that the matrix infrared absorption bands previously assigned to the anion are actually due to the NO dimer cation. This reassignment also implies that the cation has a centrosymmetric trans structure.

One-color two-photon ionization of methyl iodide, resulting in the CH3I+ and CD3I+ ions in the (X) over tilde (2)E(3/2) and (2)E(1/2) electronic states, is investigated using the zero kinetic energy (ZEKE) photoelectron technique. Unlike the conventional photoelectron spectra, the two-photon spectra are resonantly enhanced via the dissociative (A) over tilde-state continuum and exhibit an extensive vibrational structure. A long progression in the C-I stretching vibration nu 3(+) is observed, and reliable values for all the vibrational frequencies of the ions and for the ionization potentials are obtained. The appearance of the spectra is discussed in terms of consecutive two-photon absorption via a dissociative intermediate state and a time-dependent picture of spectroscopy. Experimental evidence for the influence of the asymmetric nu(6) vibration on the photodissociation process is presented. It is shown that two-photon ZEKE spectroscopy via a dissociative intermediate state can serve as a powerful probe of the photodissociation dynamics. It also allows one to explore regions of the ground-state potential energy surface of the ion that are far from equilibrium.

One-color two-photon zero kinetic energy (ZEKE)-spectra of CH3I were obtained via an intermediate resonant state. In contrast to one-photon spectra an intense progression in the totally C-I stretching mode nu3+ is observed. The observation can be explained by a resonant-Raman like enhancement in the intermediate dissociative state.

One-color two-photon zero kinetic energy (ZEKE)-spectra of CH3I were obtained via an intermediate resonant state. In contrast to one-photon spectra an intense progression in the totally symmetric C–I stretching mode ν3+ is observed. The observation can be explained by a resonant-Raman like enhancement in the intermediate dissociative state.

The nonresonant two-photon (1+1) ZEKE (zero kinetic energy) photoelectron spectrum from the X̃ 1A1 electronic ground state of H2S is reported. Complete rotational resolution of the X̃ 2B1 ground state of the ion was achieved for different temperatures in the jet. The ZEKE spectra show angular momentum transfer up to ΔN=2. The rotationalNKa+Kc++ ← J″Ka″Kc″ branching ratios for the low-lying rotational levels were determined. The strongest transitions are those with ΔKa=Ka+−Ka″=±1 and ΔKc=Kc+−Kc″=0 (type c transitions) but transitions with ΔKa=0 and ΔKc=±1 (type a transitions) also show a surprisingly high intensity. Changes in Ka or Kc up to ±3 are observed. The two-photon spectra are compared with those obtained via one-photon VUV photoionization by other authors.

The high-resolution zero kinetic energy photoelectron spectrum of CS2 is presented. Accurate values for the ionization potential and the spin—orbit splitting of the X̃ + 2Πg are obtained. Observation of the symmetry-forbidden excitations of the v2 bending vibration yields accurate frequencies for this normal mode. The Renner—Teller splitting for the Δu32 and the Σ−u components of v+2 in the upper 2Πg12 spin—orbit component has been resolved for the first time. The photoionization efficiency spectra show a strong counter-correlation of the CS+2 and S+ fragments.

The nonresonant-two-photon (1 + 1) zero kinetic energy (ZEKE) photoelectron spectrum out of the 2-PI-1/2 electronic ground state of nitric oxide is reported. The ZEKE spectra, obtained for different initial temperatures in the jet, show complete rotational resolution of the X 2-SIGMA+ electronic ground state (v+=0) of the ion. Angular momentum transfers up to DELTA-J = +/- 7/2 are observed. The rotational J+ <-- J" branching ratios determined for this ionization process from a valence state differ remarkably from those observed in two-color resonant ZEKE spectra of electronically excited Rydberg states.

The nonresonant‐two‐photon (1+1) zero kinetic energy (ZEKE) photoelectron spectrum out of the 2Π1/2 electronic ground state of nitric oxide is reported. The ZEKE spectra, obtained for different initial temperatures in the jet, show complete rotational resolution of the X 2Σ+ electronic ground state (v+=0) of the ion. Angular momentum transfers up to ΔJ=±7/2 are observed. The rotational J+←J‘ branching ratios determined for this ionization process from a valence state differ remarkably from those observed in two‐color resonant ZEKE spectra of electronically excited Rydberg states.

High resolution zero kinetic energy (ZEKE) photoelectron spectra of the NO dimer are measured. They provide information about the ionization energy of the neutral, as well as about the binding energy, vibrations and structure of the ionized dimer indicating considerable structural reorganization of the dimer upon ionization.