Garry S. Grubbs

A search accelerated correct intensity Fourier transform microwave spectrometer with pulsed laser ablation source

The ablation of metal surfaces in the presence of a precursor gas produces reaction products which are often difficult to predict and highly dependent on ablation conditions. This article describes the successful development and implementation of a laser ablation source-equipped Fourier transform microwave spectrometer capable of observing 4 GHz regions of spectra in a single data acquisition event. The dramatically increased speed with which regions may be searched, when compared to other high resolution microwave techniques, allows the source conditions to be the prime variable in laser ablation microwave spectroscopic studies. A second feature of the technique is that observed spectral features have correct relative intensities. This is advantageous when assigning observed spectra. The study of two metal chlorides, AgCl and AuCl, illustrate the instruments benefits.

Some geometric and electronic structural effects of perfluorinating propionyl chloride.

Propionyl chloride and perfluoropropionyl chloride have been characterized using chirped pulse Fourier transform microwave spectroscopy between the frequency range of 8 and 14 GHz. Molecules were studied in separate experiments in supersonic expansions of argon. The (35)Cl, (37)Cl, and each of the monoisotopic (13)C substituted isotopologues of propionyl chloride were observed. The (35)Cl and (37)Cl isotopologues of perfluoropropionyl chloride were observed. Analyses of the resulting microwave spectra have yielded spectroscopic constants for the target molecules. The analyses indicate that, under the conditions of these experiments, both molecules are only detectable as cis conformers in which angleCCCO = 0 degrees . Comparisons are made between the electronic and geometric structure of propionyl chloride and perfluoropropionyl chloride, and also other acyl chlorides. The data produced are relevant in regards to quantifying the known destabilizing effect of perfluoroalky chains on carbonyl groups. Distinct differences in electronegativity between the CH(3)CH(2)CO- and CF(3)CF(2)CO- groups are discussed. Methyl group internal rotation is observed for propionyl chloride and has been analyzed to produce a V(3) barrier height.

H2—AgCl: A spectroscopic study of a dihydrogen complex

H2-AgCl has been observed on a Fourier transform microwave spectrometer equipped with laser ablation source and determined to be a dihydrogen complex. Transitions up to J = 3-2 have been measured and analyzed for four isotopologues of the complex containing ortho and para H2. The ortho and para spin states have been included in one fit, a deviation from the typical H2 complex. Rotational constants B and C, centrifugal distortion constants Δ(J) and Δ(JK), nuclear electric quadrupole coupling constants χ(aa), χ(bb), and χ(cc) for (35)Cl and (37)Cl have been fit for both spin states while nuclear spin-nuclear spin constants D(aa), D(bb), and D(cc), and nuclear spin-rotation constant C(aa) have been reported for the ortho spin state. Quantum chemical calculations predict a strong bonding interaction and the strength of the complex has been related to reported χ(aa) and Δ(J) values amongst a host of comparable species, including the AgCl monomer itself. Bond lengths have been determined for Ag-Cl, Ag-H2 center-of-mass, and H-H and are reported.

Probing the chemical nature of dihydrogen complexation to transition metals, a gas phase case study: H2-CuF.

This work details a gas phase study of the bonding of hydrogen to the metal in a simple diatomic analogue of a metal organic framework (MOF), copper fluoride, via dihydrogen complexation. This is the first microwave study of these types of interactions. J = 1-0 transitions of para-H(2)-CuF, ortho-D(2)-CuF, and HD-CuF have been measured and analyzed. The complexes were prepared by laser ablating a metal copper rod in the presence of a gas mix of 0.6% SF(6) and 3% H(2) in Ar undergoing supersonic expansion. The binding energy of this complex is addressed through quantum chemical calculations and measured nuclear quadrupole coupling constants for copper and deuterium. The significant change in the calculated binding energy and nuclear quadrupole coupling constants in relation to similar molecules suggest bonding greater than that typical of van der Waals interactions.

The Complete Iodine and Nitrogen Nuclear Electric Quadrupole Coupling Tensors for Fluoroiodoacetonitrile Determined by Chirped Pulse Fourier Transform Microwave Spectroscopy

Molecular pulsed jet, chirped-pulse Fourier transform microwave spectroscopy has been used to record 499 transitions for the title molecule. Measurements have been made in the 8-16 GHz regions. Vibrational and electronic ground state rotational constants A, B, and C have been obtained, together with centrifugal distortion terms. The complete iodine and nitrogen nuclear quadrupole coupling tensors have been determined for the first time. Quantum chemical calculations have been performed to aid with analyses and, in particular, to aid in determining the signs of the off-diagonal components of the nuclear quadrupole coupling tensors. An experimentally determined relative electronegativity scale for several polyhalomethyl groups is proposed.

Chirped pulse Fourier transform microwave spectroscopy of 1,1,2,2-tetrafluoro-3-iodopropane

The pure rotational spectra of the two lowest energy conformers of 1,1,2,2-tetrafluoro-3-iodopropane have been investigated between the frequency limits of 7.5 and 16 GHz using chirped pulse Fourier transform microwave spectroscopy. Quantum chemical calculations have been performed to aid the spectral analyses. For the trans–trans conformer, which is calculated to be the lowest in energy, a total of 135 transitions were recorded. For the gauche–gauche conformer a total of 286 transitions were recorded. In both cases the complete iodine nuclear quadrupole coupling tensor has been determined.

Bis-trifluoromethyl Effect: Doubled Transitions in the Rotational Spectra of Hexafluoroisobutene, (CF3)2C═CH2

Rotational spectra for hexafluoroisobutene, and its (13)C isotopologues, have been recorded between 8 and 16 GHz using a chirped pulse, Fourier transform microwave spectrometer. Notably, all spectra observed are doubled with separations between the doublets being between 1 and 60 MHz. We propose that the bis-trifluoromethyl groups of the target molecule are staggered in the equilibrium configuration, and that a novel, out-of-phase rotation through a F-CCC-F planar configuration with low barrier (<100 cm(-1)), leads to the observed doubled rotational spectra.

Microwave Spectra and Structure of Ar-1,3-Difluorobenzene

The microwave spectrum of the dimer Ar-1,3-difluorobenzene from 2 to 18 GHz is reported. The spectrum has been observed using a chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer that has recently been expanded to include the 2-6 GHz region of the electromagnetic spectrum. Details of this upgraded spectrometer are reported. Eighty-seven transitions were observed for the parent dimer spectrum, which was adequately fit to a semirigid rotational Hamiltonian consisting of A, B, and C as well as four quartic centrifugal distortion constants. Observations of 13C species in natural abundance were aided by utilizing smaller chirp ranges of 7-9 and 9-11 GHz for 1.9 million and 3.73 million averages, respectively. Assignment of 13C isotopologues allowed for determination of the Kraitchman coordinates of the carbon atoms as well as inertial fits of the complex. The quantum-chemical structure predicts an Ar to monomer center of mass distance of 3.48 Å, compared with 3.564(1) Å determined from experimental structural analysis. This new study indicates that in fluorinated benzene-Ar dimers, when the fluorines are separated by more carbon atoms, the Ar-ring center distance decreases.