D. Bellert

The ground state of CoAr

Abstract Rotationally resolved photodissociation spectra of CoAr + have been observed for three different electronic transitions of the isolated ion. Analysis yields rotational constants and the angular momentum (spin plus orbit) for both states in the transition. The bond length of the vibrationless ground state of this ion is determined to be r 0 =2.385 ±0.005 A consistent with a 3 Δ 3 electronic state. Three assigned excited-state diabatic dissociation limits enable the accurate determination of the adiabatic binding energy of ground state of CoAr + as D 0 =4111±5 cm −1 . These values are discussed in comparison with recent ab initio theory.

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 bond length of ZrAr

Abstract The photodissociation spectrum of isolated ZrAr + has been observed. The bond length in the vibrationless ground state is r 0 = 2.718 ± 0.01 A with Ω″ = 3 2 . The c state of this ion has Ω′ = 5 5 , an electronic origin at T 00 = 15580 cm −1 , a vibrational frequency of ω e = 74.9 cm −1 , an anharmonicity of ω e x e = 1.15 cm −1 , an equilibrium rotational constant of B e = 0.0655, and a rotation-vibration constant of α e = 0.00154 cm −1 . The bond length of this excited state is r 0 = 3.050 ± 0.01 A with a diabatic bond energy of 1170 ± 20 cm −1 . Assignment of the c-X band convergence places the adiabatic binding energy of ground state of ZrAr + at D 0 = 2706 ± 20 cm −1 .

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 .

THE PHOTODISSOCIATION OF V+.CH4

Abstract The isolated VCH 4 + ion has been interrogated via resonant one-photon photodissociation spectroscopy. An electronic transition corresponding to a 3d 3 4s ← 3d 4 excitation of the metal center characteristic of electrostatic complexes of V + is observed. The vibronic structure of the spectrum yields the stretching frequency of the excited state of the complex, 90.0 cm −1 , with a diagonal anharmonicity of 0.70 cm −1 as well as a rocking frequency of 44.8 cm −1 . The electrostatic binding energy of the excited metal ion (3d 3 4s) to methane is determined to be 2900 ± 300 cm −1 , whereas the ground state metal ion (3d 4 ) is bound by 5250 ± 300 cm −1 .

SPIN FORBIDDEN TRANSITIONS IN NIAR

Abstract Quartet—doublet optical transitions in the isolated NiAr+ ion have been observed by photodissociation excitation spectroscopy. Three low-lying quartet states correlating to two different spin—orbit components of the Ni+ d8s (4Fj) + Ar(1S) dissociation limit have been characterized and the vibrational frequency, anharmonicity, and diabatic binding energy of these states has been measured. The adiabatic binding energy of the ground state of the ion is accurately determined from the two excited limits as 4572 ± 5 cm−1, more than twice the diabatic binding of the excited quarter states. The mechanism for the photodissociation of the excited states is found to involve coupling between adjacent spin—orbit components of the quartet asymptote.

THE STRUCTURE OF CO+. OCO

Abstract Rotationally-resolved resonant photodissociation of isolated Co·OCO+ ions has been observed for the first time. Analysis of low energy A 3 Φ 4 ← X 3 Δ 3 and a 1 Δ 2 ← X 3 Δ 3 electronic transitions confirm the linear geometry for at least these three electronic states of the complex. The zero-point level of the ground 3 Δ 3 state exhibits a rotational constant of 0.05699±0.0005 cm−1 consistent with a center-to-center distance between the metal atom and the ligand (the Co+–C distance) of 3.17±0.01 A. This experimental result agrees completely with recent ab initio predictions of the ground-state geometry of this molecule.

A measure of the effective electric-dipole polarizability of argon

Abstract The electric dipole polarizability has been determined in a unique way. Binary complexes of argon with transition metal cations have been studied by optical spectroscopy. The vibrational structure of electronic transitions near the dissociation limit of the upper state quantifies the forces between the atoms. The polarizability of argon is determined from the charge-induced-dipole force in four different molecular ions as 1.49 ± 0.10 A 3 . This is lower than the accepted value by 9%. This discrepancy may imply that the multipole expansion of the charge distortion does not have linearly independent coefficients in the field of an ion at close range. Induced higher-order moments appear to reduce the effective dipole polarizability.

The bond strength of Ni+2

Abstract The bond dissociation energy, D 0 , of Ni + 2 is estimated to be 2.32 ± 0.02 eV from the onset of rapid predissociation in the resonant two-color photodissociation (R2CD) spectrum. This predissociation manifests itself in an abrupt change in the lifetimes of some of the upper states above the adiabatic dissociation limit but without the onset of continuum absorption or noticeable broadening of spectral features. The value of the bond strength determined by this study is larger than that of the neutral molecule by 0.25 eV, in rough agreement with literature theoretical predictions.