Andrew M. Ellis

High resolution electronic spectroscopy of ZnCH3 and CdCH3

ZnCH3 and CdCH3 radicals have been prepared in a cold supersonic free jet expansion and their laser‐induced‐fluorescence spectrum recorded for the Au20092E←Xu20092A1 electronic transition. These spectra show well resolved rotational and spin structure, which has been completely analyzed. This analysis yields the rotational constants and the components of the spin–rotation tensors in the A and X states of both radicals. The observed constants are discussed in terms of the electronic structure of the radicals. It is demonstrated that the upper F2 spin–orbit component of the Au20092E state of CdCH3 is strongly perturbed by another, dissociative electronic state. This leads to some predissociation of the Au20092E3/2 component and a broadening of its lines. The rotational and fine structure in this state is also quite perturbed leading to an unusual, but still interpretable spectrum.

Spectroscopy of jet‐cooled metal–monocyclopentadienyl complexes: Laser excitation spectra of calcium and cadmium cyclopentadienides

A laser vaporization/photolysis technique for obtaining spectra of jet‐cooled organometallic molecules is reported. It makes use of an excimer laser which vaporizes a metal sample and simultaneously photolyzes an organic precursor passing over the surface of the metal. The metal atoms and organic fragments then react to yield the organometallic species. In principle, this approach could be used to prepare a wide variety of gas‐phase compounds of any metal for spectroscopic study. To illustrate its capabilities, laser excitation spectra of the monocyclopentadienide and monomethyl derivatives of Ca and Cd are presented. In the case of cadmium cyclopentadienide, this report constitutes the first spectroscopic observation of this molecule.

High-temperature photoelectron spectroscopy. A study of niobium monoxide and tantalum monoxide

The He I photoelectron spectra of NbO and TaO have been recorded. In both cases four main bands were observed which can be attributed to ionization of the isolated metal monoxide molecule. Bands associated with other oxides or the metal were not observed.Assignment of the photoelectron spectra of NbO and TaO was made with the aid of Hartree–Fock–Slater (HFS) calculations and by comparison with the known photoelectron spectrum of VO. The first adiabatic ionization energies of NbO and TaO have been measured as 7.91 ± 0.02 eV and 8.61 ± 0.02 eV, respectively. Suggestions are made to explain the poor agreement between previous mass-spectrometric values for the first ionization energy of each oxide.

Vacuum ultraviolet photoelectron spectroscopy of transient species. Part 18.—The cyclopropyl, isopropyl and n-propyl radicals

Bands associated with the first ionization energies of the cyclopropyl, n-propyl and isopropyl radicals have been studied using a multidetector photoelectron spectrometer. In each case vibrational fine structure was recorded which was assigned with the aid of ab initio molecular-orbital calculations and force-field calculations. For the cyclopropyl radical the adiabatic and vertical ionization energies were measured as 8.18 ± 0.03 and 8.86 ± 0.02 eV, respectively. Regular vibrational structure, with an average spacing of 1000 ± 70 cm–1, is assigned to excitation of the pyramidal bending mode at the α-C-H position in the cyclopropyl ion. In the n-propyl and isopropyl cases spectra which are an improvement over those previously available have been obtained, and in both cases vibrational structure attributable to excitation of CCC bending modes in the ion have been resolved in the first photoelectron bands.

Laser-induced fluorescence spectra of the cold radicals, ZnCH3 and CdCH3, and their inert-gas complexes, XCdCH3 (X = He, Ne, Ar, Kr, Xe)

Abstract Electronic spectra of the radicals ZnCH 3 and CdCH 3 cooled in a free jet expansion are reported. Possible assignments of the vibronic features observed are given. A preliminary spectroscopic study of the inert-gas radical van der Waals complexes Xue5f8CdH 3 (X = He, Ne, Ar, Kr, Xe) is also reported.

Dispersed fluorescence spectroscopic study of the ground electronic state of silver trimer

Abstract Dispersed fluorescence spectra of Ag 3 have been recorded for the first time. The experimental data provide the first clear determination of the fundamental vibrational frequencies of the trimer in its ground electronic state, i.e. ν 1 ≈ 180 cm −1 and ν 2 ≈ 67 cm −1 , and also lead to a reassignment of previous Raman work on the molecule. Evidence of significant Jahn—Teller activity in Ag 3 is clearly demonstrated by the observation of a progression in the nominally degenerate bending vibrational mode, ν 2 , in both the excitation and dispersed fluorescence spectra. Our observations are consistent with ab initio calculations which have predicted that the triangular 2 E′ ground electronic state should undergo significant Jahn—Teller distortion.

Dispersed fluorescence spectroscopy and fluorescence lifetime measurements of excited vibrational levels of CdCH3

Abstract Laser-induced excitation and dispersed fluorescence spectra (originating from the 0 0 , 2 1 and 3 1 vibrational levels of the A electronic state) of jet-cooled CdCH 3 are presented and assigned. The observation of emission from these levels is a result having important implications for the dynamics of photodissociation of Cd(CH 3 ) 2 . Fluorescence lifetimes for emission from the 0 0 , 2 1 and 3 1 vibrational levels are also presented.

Electronic spectroscopy of jet-cooled half-sandwich organometallic free radicals: laser-induced fluorescence study of the monomethylcyclopentadienyl complexes of zinc and cadmium

Laser excitation and single vibronic level fluorescence spectra have been obtained for the open-faced sandwich complexes methylcyclopentadienylzinc and methylcyclopentadienylcadmium, ZnC5H4CH3 and CdC5H4CH3, respectively. These molecules are produced in a supersonic jet expansion using a laser vaporization/photolysis technique. Two nearby excited electronic states were observed in the excitation spectra. These two states arise from splitting of the A2E1 states of ZnC5H5 and CdC5H5 owing to the lower symmetry of the metal methylcyclopentadienyl complexes. In the case of CdC5H4CH3, a third electronic state was also identified. Both laser excitation and dispersed fluorescence spectra of these molecules show extensive vibrational structure originating from both skeletal and intra-ring vibrations. From these features, we were able to determine where the metal atom is most likely located, i.e. above the ring in a ring-bonding (η5) fashion. In addition, we also observe low-frequency modes which we attribute to hindered rotation of the methyl group. Barriers to methyl free rotation and changes in conformation of the methyl group were determined from this structure. This report constitutes the first spectroscopic study of these free radicals and the first detailed investigation of methyl torsional barriers in open-shell organometallic molecules.