Dan Lessen

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.

On the nature of NiAr

Abstract NiAr+ ions generated in a supersonic expansion of Ni+ with a 1% Ar/He carrier gas are injected into a tandem mass spectrometer and photodissociated with visible tunable laser radiation. A photofragmentation feature observed at 17984 cm− is believed to correspond to the dissociation threshold of NiAr+ to excited state (2F 7 2) Ni + and ground state Ar. This assignment yields a prediction of 0.55 eV for the binding energy (D00) of NiAr+. The 58NiAr+/60NiAr+ isotope shift of this spectral feature indicates the vibrational frequency in the ground state of NiAr+ to be 235± 50 cm−. Thus NiAr+ is a surprisingly “stiff” and strongly bound diatomic, discussed in light of a simple electrostatic (charge-induced-dipole) model of the internuclear forces in this class of molecules.

The unique stability of CoAr6+: Coordination complex or close-packed structure?

Cobalt atomic ions (Co+) generated in a laser-driven plasma and expanded supersonically with 10% Ar/He serve as the nucleation site for the production of cobalt argon cluster ions, CoArn+, 1 ⩽ n < 20. Under mild expansion conditions (p0d < 1 Torr cm) these ions have sufficient internal energy to dissociate prior to mass analysis. Under these conditions a particular cobalt argon cluster, CoAr6+, dominates the observed mass distribution. The possible nature of CoAr6+ is discussed.

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 .

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.

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.

Threshold photodissociation of Cr+2

Abstract A one-photon photodissociation threshold for supersonically cooled Cr + 2 is determined to be 2.13 eV. This threshold provides a strict upper limit to the adiabatic binding energy of the ground state of chromium dimer cation if the initial internal energy of the parent ion may be neglected. From the difference in the IPs of chromium atom and dimer, an upper limit to the dissociation of Cr 2 is placed at 1.77 eV.