Excited states of gaseous ions. IV. Potential energy surfaces of the H2O+ ion

Cross-sections of the potential energy hypersurfaces are reported for the four lower-lying states of the H₂O⁺ molecular ion. The symmetric dissociation of the ion has been investigated using the CNDO/2 method supplemented by a configuration interaction calculation. Self-consistent-field wave functions were calculated for the asymmetric dissociation using an extended basis of Gaussian-lobe functions. The values of the hydrogen exponents are found to be very sensitive to the molecular geometry. The calculated equilibrium H-O-H angle is 123° in the X?²B₁ state, nearly 180° in the X?A²A₁ state and 69° in the B?²B₂ state. The lower-lying quartet á ⁴B₁ is line entirely repulsive. The potential energy surface of the à ²A₁ state has a peculiar shape, characterized by two dissociation valleys.     

Excited states of gaseous ions. Transitions to and predissociation of the CΣu state of n2

A configuration interaction study of different electronic states of N⁺₂ has been performed. The position in energy and the relative intensity of the photoelectron bands of the ²Σ⁺_u states has been calculated and compared with experiment. The C²Σ⁺_u state is predissociated by a ⁴Π_u state, as previously supposed. However, owing to the attractive nature of the ⁴Π_u state a double crossing occurs. Several predissociation mechanisms of the C state can therefore take place; their lifetimes have been calculated.     

The rotational predissociation of the CH4+ and CD4+ ions

The metastable transitions producing CH₃³/CH₄ and CD₃⁺/CD₄ have been investigated by means of translational spectroscopy. For the first time structures are observed in a metastable peak corresponding to the dissociation of a polyatomic ion. They are interpreted by tunneling through a rotational barrier from discrete quasi-bound states. Kinetic energy releases have been measured.     

The lowest states of the O3+ ion

A CAS SCF calculation of the potential surfaces for the lowest states of the O₃⁺ ion is reported. An assignment of the bands in the HeI photoelectron spectrum is based upon calculated vibration profiles. This assignment shows the ground state of the ion to have ²B₂ symmetry. Also the weak bands at 15.6, 16.5 and 17.5 eV are reassigned.     

Collision- and non-collision-induced predissociation in the appearance of S+ and CS+ ions from CS2 under electron impact

Metastable transitions in CS⁺₂ leading to S⁺ + CS and CS⁺ + S under electron impact on CS₂ ae reported. The predissociation processes able to explain the occurrence of these metastable transitions are discussed. An interpretation of some fast dissociation processes is suggested.     

Effect of bending on the predissociation dynamics of N2O+

In this paper we introduce a modified version of the infinite-order sudden approximation (IOSA) for rotational and bending degrees of freedom, together     

Some ab initio calculations related to the predissociation of the C2Σu+ state of N2+

Ab initio calculations in the “first-order wavefunction” CI approximation have been performed for several states of N₂⁺ with ²Σ_u⁺, ²Σ_u^?, ⁴Π_u symmetry. A calculation of the electronic factor of the vibronic interaction between the B²Σ_u⁺ and C²Σ_u⁺ states seems to support the suggestion of Tellinghuisen and Albritton that the C state is predissociated by the continuum of the B state through nuclear momentum coupling.     

Theoretical study of the metastable peaks corresponding to the rotational predissociation of the CH4+ and CD4+ ions

Semiclassical calculations on diatomic type models are presented in order to account for the kinetic energy released in the metastable dissociation of the CH₄⁺ and CD₄⁺ ions; the discrete structure of the metastable peaks is considered.     

Low-lying states of cs22+

Using an MC SCF CI method, wavefunctions for the ground state ¹∑⁺_g and the excited states of the symmetries ¹∑⁺_g, ¹Π_g, and ¹Δ_g of the Cs²⁺₂ ionic system are generated. The potential curves for eleven ¹∑⁺_g twelve ¹Π_g, and six ¹Δ_g states are calculated. Results suggest a small charge-transfer cross section for the reaction CS⁺ + Cs⁺ → Cs CS²⁺.     

Delayed predissociation and collision-induced processes of the ammonia di-cation NH32+

Reactions of NH₃²⁺ di-cations, observed a few microseconds after formation by electron ionisation of ammonia, have been studied in a double-focusing mass spectrometer using techniques of ion translational energy spectroscopy. Fragmentation reactions occuring under unimolecular conditions correspond to predissociation processes, but lack of knowledge about states of NH₃²⁺ precludes any definitive interpretation. A partial tentative interpretation, using arguments by analogy with isoelectronic neutral species, is proposed. Almost all collision-induced fragmentations required electron transfer forming NH₃⁺ as an intermediate step, so the non-dissociative electron transfer processes were also studied. The most unexpected collision-induced fragmentation reaction was that which formed H₃⁺ fragment ions.     

Hydration of the ions Al3+ and Cu2+. An ab initio SCF study

Ab initio calculations are reported for the systems Al(H₂O)_n³⁺ and Cu(H₂O)_n²⁺ with n up to 7. The calculated binding energies increase monotically up to n = 6, with equal binding energies for n = 6 and 7 for the Al³⁺ cation. An estimate of the enthalpy of hydration of Al³⁺ is given, based on model calculations with one or two water molecules from the second solvation shell. An SN1 (dissociative) mechanism for the exchange of the water molecules from the first hydration shell of Al³⁺ appears energetically favorable if the leaving molecule remains in the second hydration shell.     

Ab initio potential curves for the lowest 1Σ+ and 3Π states of the ion CN+

Ab initio configuration-interaction calculations using a 9s5p|3s2p gaussian basis supplemented with polarization functions are presented for potential curves for the a ¹Σ⁺ and the lowest ³Π state of CN⁺. The two states are very close in energy and calculations at this level do not give an unequivocal indication of the identity of the ground state.     

The rotational predissociation of HeH+: energy and lifetime measurements

Relative lifetimes and energies above the dissociation limit have been determined for the rotational predissociation of several quasibound levels of the X¹ Σ⁺ state of ⁴HeH⁺. In particular the lifetimes are very sensitive to the shape of the potential energy curve. These measurements are used to discriminate between two ab initio potential curves, which differ by only 0.00004 au (≈ 1 meV). Using the lifetime data, relative population factors were determined for the observed levels.     

Wavelength-resolved fluorescence lifetimes of gas-phase ions: CO2+ and CS2+

A method is described for measuring wavelength-resolved fluorescence lifetimes of ions formed by HeIα photoionization, using electric-field drift of the ions in competition with fluorescence. Fluorescence lifetimes of 216 and 232 ns for the 357 nm and 378 nm peaks of N₂O⁺, and 3.5 μs for the à → X? band of CS₂⁺, were measured. The wavelength-resolved à → X? band of CO₂⁺ showed no significant dependence of fluorescence lifetime on V′, but there is some indication of variation in the CS₂⁺ lifetimes in the à → X? band.     

Catalytic oxidation of ascorbic acid by molecular oxygen in aqueous pyridine in the presence of Co2+, Ni2+, Mn2+ and Zn2+ ions

In aqueous pyridine solutions, Co²⁺, Ni²⁺, Mn²⁺ and Zn²⁺ effectively catalyze the oxidation of ascorbic acid by molecular oxygen. A kinetic expression consistent with the experimental data is given and a possible mechanism proposed.

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Theoretical study of the 2Σu+ and 2Σg+ states of Li2− and Na2−

Ab initio calculations are performed to obtain potential energy curves for the X¹Σ_g⁺ state of Li₂ and Na₂ and the X²Σ_g⁺ and A²Σ_g⁺ states of their anions. The A²Σ_g⁺ M₂^? curves are found to intersect the X¹Σ_g⁺M₂ curves at low energies and are expected to play a major role in the e^? + M₂ → M^? + M process.     

Coincidence studies of fluorescence and dissociation processes in electronic excited states of I2+, Br2+, IBr+ and ICl+

The PIFCO technique in which mass-selected photoion—fluorescence photon coincidences are counted, was used to investigate whether I₂⁺, IBr⁺ and ICl⁺ fluoresce. Measurements were made of lifetimes and fluorescence quantum yields of electronic excited states of these ions. Emission was discovered for I₂⁺ and IBr⁺, but ICl⁺ apparently does not fluoresce. Information on the radiative properties of Br₂⁺ was obtained as a by-product of the work on IBr⁺. Fragment ion kinetic energy releases were determined and provide information on dissociative ionization processes in the halogen and interhalogen ions studied.     

Double electron transfer reactions of CO22+ ions

Time-of-flight techniques have been used to measure fast neutral CO₂ products from double electron transfer reactions of CO₂²⁺ ions with 4.0–7.0 keV impact energies. Double electron transfer cross sections have been determined to be in the range of (1.1–12.5) × 10^?16 cm² for reactions of CO₂²⁺ ions with CO₂, CO, N₂, Ar and O₂.     

The first two excited 1Σg+ states of Cs2

Laser-induced fluorescence Of Cs₂ molecules in the infrared region (4000–9000 cm^?1) has been observed using several exciting wavelengths from an argon-ion laser and from a ring dye laser. Accurate molecular constants for the first two excited ¹Σ_g⁺ electronic states are derived from spectra recorded at high resolution by Fourier transform spectroscopy. Main molecular constants are: (2)¹Σ_g⁺: T_c = 12114.090 cm^?1, ω_e = 23.350 cm^?1, B_c = 7.4.5 × 10^?3 cm^?1, R_c = 5.8316 Å; (3)¹Σ_g⁺: T_e = 15975.450 cm^?1, ω_e = 22.423 cm^?1 , B_e = 8.23 × 10^?3 cm^?1, R_c = 5.5569 Å.