R.L. Asher

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.

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 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 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 .

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.

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.

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.