P.J. Brucat

Resonant photodissociation of CoAr+ and CoKr+: Analysis of vibrational structure

The transition‐metal rare‐gas diatomic ions, CoAr+ and CoKr+, generated and cooled in a supersonic expansion, are studied by visible resonant photodissociation for the first time. Photofragmentation excitation spectra exhibit sharp vibronic features which are members of several excited electronic state vibrational progressions in each molecular ion. Analysis of over 200 vibronic transitions in these spectra reveals details of the potential‐energy surfaces characterizing the bonding in these excited states. The adiabatic ground‐state dissociation energies of CoAr+ and CoKr+, determined as 4100 cm−1 and 5400 cm−1, respectively, are ca. 37% larger than the diabatic dissociation energy of an excited state which dissociates into 3d8 3P2 Co+1S Ar(Kr) excited atoms and 95% larger than a state dissociating into 3d74s 3F2Co+1S Ar(Kr) atoms. Vibrational frequencies, anharmonicities, electronic origins, and dissociation limits of three electronic states in each molecule have been determined. A simple electrostatic b...

Vibrational structure of an electrostatically bound ion–water complex

Supersonically cooled VH2O+ is resonantly one‐photon dissociated in the visible region. An excited state vibrational progression in the V+(OH2) stretching mode is observed with a frequency W’e=339 cm−1 and an anharmonicity We X’e =4.5 cm−1. Analysis of the spectra of isotopically substituted species places an estimate of the ground state ion–water stretch at 420±75 cm−1. The electronic origin of the upper state places a strict upper limit to the adiabatic binding energy of this complex at 1.97 eV.

Characterization of transition metal–rare‐gas cations: VAr+ and VKr+

Resonant photodissociation of supersonically cooled and isolated VKr+ reveals a vibronic progression of a single electronic transition in the visible spectrum. Vibrational analysis of these data indicates an upper state vibrational frequency of 99 cm− 1 and a diabatic upper state binding energy of 0.26 eV. Assignment of the dissociation limit of this upper state at 17 419 cm− 1 to V+(3d 84s 5 P 2)+Kr(1 S 0) places the adiabatic binding energy of the ground state of VKr+ at 0.49 eV. The spectrum of VAr+ is analogous to that of VKr+ but shows a somewhat reduced ground state adiabatic binding energy for this molecule, 0.38 eV. A simple inductive binding model is proposed to predict the geometries of these species and parametrize the metal–rare‐gas interatomic potential. This potential is used to gain insight into the factors contributing to the enhanced stability of the ‘‘coordinatively saturated’’ complexes, VAr+ 4 and CoAr+ 6.

Energy dependent photochemistry in the predissociation of V(OCO)

Photofragmentation of the V(OCO)+ molecular ion in the visible shows sharp resonant absorption features and two distinct dissociation pathways: V+(OCO)+→V++CO2 and V(OCO)+→VO++CO. The photodissociation excitation spectrum reveals two low frequency vibrational modes in the upper state of this molecule at 105 and 196 cm−1. This spectrum indicates that the same photoexcited state in V(OCO)+ is the precursor to both V+ and VO+ products. The branching ratio for VO+/V+ production depends on the excitation energy and upper state vibrational mode. An estimate of the barrier to the production of VO+ of 13 000 cm−1 (37 kcal/mole) above the ground state of V(OCO)+ is made from this data.

The CX transition in CaKr+ and CaAr+

Abstract An electronic transition in the isolated CaKr + ion with an origin at 14217 cm −1 has been observed in the resonant photodissociation spectrum. A short vibrational progression yields excited state vibrational constants of ω ′ e = 60 cm −1 and ω e x ′ e = 2.78 cm −1 and a diabatic binding energy of 330 ± 100 cm −1 . The excited state in this transition arises from the Ca + 3 p 6 3 d [ 2 D ] + Kr [ 1 S ] atomic limit and is tentatively assigned as a 2 Σ + state. A single weak hot band feature places the ground state vibrational frequency, ΔG″ 1 2 , at 74 cm −1 . The analogous transition in CaAr + has also suffered analysis. The X 2 Σ + ground state of the CaKr + ion is bound by 840 ± 100 cm −1 almost the same as that found for CaAr + , 890 ± 100 cm −1 .

The Co+·CO2 electrostatic complex: Geometry and potential

Abstract The electrostatic complex of Co+ with a single CO2 molecule is studied by optical excitation of a 3d74s—3d8 transition centered on the metal ion. Excited-state vibrational information is used to characterize the diabatic molecular potential in terms of spectroscopic constants. Two vibrational frequencies and five anharmonicity constants characterize the forces of complexation, all of which have been determined experimentally. Analysis of the rotational contours indicates the complex is linear in its ground electronic state with a Co+-C separation of 3.30 A (the smaller Co+-O distance: 2.14 A) in the zero-point level of the complex.

THE BINDING ENERGY OF NI+.CO2

Abstract The internally cold, gas-phase electrostatic complex of Ni + with a single carbon dioxide molecule, Ni + ·OCO, is observed by resonant photodissociation spectroscopy with visible light. Sharp bound—bound optical absorptions are detected via predissociation into Ni + and CO 2 fragments. A cutoff in the photofragmentation is observed below 17100 cm −1 and this represents the threshold for dissociation into the lowest quartet pathway. This places the binding energy of the Ni + ·OCO complex at 1.08±0.01 eV with respect to ground state Ni + and CO 2 .

Spectroscopically determined binding energies of CrAr+ and Cr(N2)+

Abstract Supersonically cooled CrAr + and Cr(N 2 ) + are photodissociated in the visible region. Diabatic dissociation thresholds are observed enabling the ground state binding energy to be determined as 0.61 ± 0.04 and 0.29 ± 0.04 eV for Cr(N 2 ) + and Cr(Ar) + , respectively. These data are compared with previously determined binding energies of first row transition-metal rare-gas diatomics.

The bond length of CoKr

Abstract Rotationally resolved photodissociation spectra of CoKr + have been observed for an electronic transition in the isolated ion. Analysis yields rotational constants and the angular momentum (spin plus orbit) for both states in the transition. The bond length in vibrationless level of the ground state of this ion is determined to be r 0 = 2.447 ± 0.005 A with a rotational structure consistent with a 3 Δ 3 electronic state. Excited-state diabatic dissociation limits enable the determination of the adiabatic binding energy of ground state of CoKr + as D 0 = 5405 ± 15 cm −1 . These data are discussed in comparison with similar observations in CoAr + and CoXe + .

Resonant two-photon dissociation of Ni2+

Abstract Ni 2 + ions generated in a pulsed high-temperature plasma and cooled by supersonic expansion are photodissociated with tunable visible laser radiation. Resonant bound-bound absorption in the isolated ion is detected by the observation of Ni 2 + → Ni + + Ni sequential two-photon dissociation. Progressions of vibronic bands with partially resolved rotational structure belonging to several distinct electronic transitions in Ni 2 + have been observed in the interval between 16250 and 23500 cm −1 . The appearance and preliminary analysis of this resonant two-photon dissociation (R2PD) spectrum will be discussed.