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We have measured the spectrum of laser photodissociation of OH+ molecular ions to O + H+ and O+ + H fragments for photon energies of 38 100–40 900 cm−1. The OH+ ions were stored as a fast beam (5.50 MeV) in the storage ring TSR for several seconds to achieve rovibrational cooling into the lowest rotations N′′ = 0–11 of the vibrational ground state X3Σ−(v ′′ = 0), close to room temperature (≈300 K). The many resonances in the spectra reveal the energies, widths, and O/O+ branching ratios of 44 predissociating quasibound levels (Feshbach resonances) that lie between the fine-structure states of the O fragment and belong to the last, near-threshold vibrational states v ′ = 9 and 10 of the A3Π electronic state. For the A3Π0,1 substates, isolated levels with v ′ = 11 are observed and attributed to double-well distortions of these curves due to nonadiabatic interactions. Another five isolated levels are assigned to the v ′ = 0 and 1 states of the shallow 15Σ− electronic state, borrowing oscillator strength from nearby A3Π levels. Together, the near-threshold levels deliver a new value D0 = 40 253.8(1.1) cm−1 for the dissociation energy of OH+. Through a two-step photodissociation process, 72 levels from the lower bound states A3Π(v ′ = 7–8) appear as well and are rotationally analyzed. The level energies are used to construct improved A3Π and 15Σ− Born-Oppenheimer potentials. The totality of the spectral data (energies, widths, intensities, and branching ratios) can provide tight constraints for the potentials and nonadiabatic interactions assumed in future coupled-channel calculations of OH+ photodissociation or of the related charge-exchange reaction O + H+ → O+ + H. [ABSTRACT FROM AUTHOR]

We report on the application of an electrostatic ion beam trap as a mass spectrometer. The instrument is analogous to an optical resonator; ions are trapped between focusing mirrors. The storage time is limited by the residual gas pressure and reaches up to several seconds, resulting in long ion flight paths. The oscillation of ion bunches between the mirrors is monitored by nondestructive image charge detection in a field-free region and mass spectra are obtained via Fourier transform. The principle of operation is demonstrated by measuring the mass spectrum of trapped Ar(super +) and Xe(super +) particles, produced by a standard electron impact ion source. Also, mass spectra of heavier PEG(sub n)Na(super +) and bradykinin ions from a pulsed MALDI ion source were obtained. The long ion flight path, combined with mass-independent charge detection, makes this system particularly interesting for the investigation of large molecules.

Rate coefficients for dissociative recombination of [HD.sup.+] in selected vibrational states have been measured by a combination of two molecular fragment imaging methods by using the heavy-ion storage ring technique. Recombination fragment imaging yields state-to-state reaction rates. These rates are converted to rate coefficients by using vibrational level populations of the stored ion beam, derived from nuclear coordinate distributions measured on extracted ions. The results show strongly increasing rate coefficients for high vibrational excitation, where additional dissociation routes open up, in agreement with a theoretical calculation. Very low rate coefficients are found for certain, isolated vibrational states., The last 20 years have seen tremendous progress in our understanding of elementary chemical reactions. Molecular-beam experiments have provided very detailed information about the dynamics of inelastic and reactive collisions [...]

We have measured the photodissociation spectrum of CH+ and CD+ molecular ions, stored as fast (MeV) ion beams in the heavy-ion storage ring TSR. Several b 3Σ--a 3Π bands were observed as strong resonances because a large fraction of the ions in the metastable a 3Π(v=0) state were pumped to b 3Σ- levels and predissociated via the c 3Σ+ state into C+ and H(D) fragments. From a rotational analysis of the 2-0, 3-0, and 4-0 bands in CH+ and the 3-0 and 4-0 bands in CD+, we derive spectroscopic constants for these levels and also revise a previous analysis of the 0-0 and 1-0 bands in CH+. Combining all data delivers new, significantly adjusted equilibrium constants for the b 3Σ- and a 3Π electronic states. Apart from the spectroscopic analysis, we estimate the predissociation rates of the upper b 3Σ- vibrational levels in CH+ and compare them to a model. For the initial rovibrational distribution of the stored metastable CH+ molecules, the data indicate a faster vibrational cooling than derived before, and rotational cooling at a rate similar to the X 1Σ+ ground state. New aspects of the spin-forbidden a 3Π-X 1Σ+ radiative decay are discussed. Finally, we predict b 3Σ--a 3Π absorption and a 3Π-X 1Σ+ emission lines through which CH+ in the metastable a 3Π(v=0) state might be detectable in astrophysical environments. [ABSTRACT FROM AUTHOR]

Vibrational relaxation and isomerization of internally excited deuterated formyl and isoformyl cations has been investigated on the time scale of 2 ms to 12 s using the nearly interaction-free environment of an ion storage ring. De-excitation of the v[sub 2] bending modes of DCO[sup +] and DOC[sup +] due to spontaneous radiative transitions was observed as a function of the storage time by measuring their foil-induced Coulomb explosion using three-dimensional coincident fragment imaging. No isomerization of low-lying vibrational levels of DOC[sup +] ions was observed on the time scales considered. By comparing the Coulomb explosion data to molecular bond angle distributions obtained from vibrational wave function calculations, the time evolution of the mean v[sub 2] population is deduced for both isomers. The stored DOC[sup +] ions are found to thermalize with the 300 K black-body radiation, while relaxation of the DCO[sup +] bending vibrations was found to require considerably longer times, in agreement with a predicted very small transition moment of the v[sub 2]=1 level. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Absolute cross sections for photodetachment of negative carbon clusters are reported for [C. sup. -][C. sub. n] (n = 3, ..., 8). The results indicate that various neutral isomers exist, some with electron affinities as low as 1 electron volt. The method of production plays an important role in the characteristics of carbon clusters., Pure carbon molecules are currently under intense experimental and theoretical scrutiny. These molecules are believed to play an important role in the formation of soot in flames and have been [...]

The structures of ethynyl and acetylene cations were investigated utilizing the Coulomb explosion imaging method. The geometrical probability density functions for the bending modes were obtained for the protonated and deuterated forms of each species. Detailed analyses of the data reveal that both the measured linear equilibrium geometries and the observed extent of the correlated bending vibrations agree with ab initio calculations for C2H+2 and C2D+2. C2H+ and C2D+ are found to be linear, but the extent of the bending amplitudes are by far larger than the corresponding theoretical predictions. [ABSTRACT FROM AUTHOR]

A quantitative analysis of the bending mode of H2O+ is made using the Coulomb Explosion technique. The full extent of the angular distribution is measured and is in good agreement with the previously measured bending frequency. The equilibrium value for the angle is extracted from the data with high precision and is in excellent agreement with theoretical predictions as well as spectroscopic measurements. [ABSTRACT FROM AUTHOR]

The Coulomb explosion imaging (CEI) technique has been applied to a beam of vibrationally cold CH2+ molecular ions and the distribution of bond angles was extracted. From these data, we are able to demonstrate conclusively that the electronic ground state potential of this molecule has a C2v minimum and that the zero-point energy lies below the potential barrier to linearity. [ABSTRACT FROM AUTHOR]