Robert L. Kuczkowski

Molecular structures of gas‐phase polyatomic molecules determined by spectroscopic methods

Spectroscopic data related to the structures of polyatomic molecules in the gas phase have been reviewed, critically evaluated, and compiled. All reported bond distances and angles have been classified as equilibrium (re), average (rz), substitution (rs), or effective (ro) parameters, and have been given a quality rating which is a measure of the parameter uncertainty. The surveyed literature includes work from all of the areas of gas‐phase spectroscopy from which precise quantitative structural information can be derived. Introductory material includes definitions of the various types of parameters and a description of the evaluation procedure.

The microwave spectrum of argon-phosphorus trifluoride

Several van der Waals complexes with a high atom percentage of fluorine have been studied by high-resolution techniques. Examples include BF3-N2 [ 11, HCFs bonded to an acid or ammonia [ 2,3], COF2-Ar [ 41, ClF-Ar [ 5 1, and a number of HF complexes [ 61. Most of the systems are linear or symmetric tops. Usually the fluorine atoms are distant from the second species and do not appear to directly interact with it. Ar-COF2 is an exception; it is an asymmetric top (of necessity) with the Ar located above the CF2 triangle. We report here the microwave spectrum of the Ar-PFX complex which is also an asymmetric top. In this complex, the fluorine is closer than phosphorus to the argon atom.

The microwave spectrum, structure, and tunneling motion of the sulfur dioxide dimer

The microwave spectrum of (SO2)2 has been reinvestigated using a pulsed beam Fourier‐transform microwave spectrometer. Several new a‐type transitions for the normal species and the a‐type spectra of eight isotopically substituted species were measured. The spectra indicate that the SO2 dimer undergoes a high‐barrier tunneling motion. Based on the analysis used for (H2O)2 by Coudert and Hougen [J. Mol. Spectrosc. 130, 86 (1988)], the internal motion is identified as a geared interconversion motion similar to that displayed by (H2O)2. From the analysis of the moments of inertia of the various isotopic species, an ac plane of symmetry is established for the dimer and the tilt angles of the C2 axes of each subunit relative to the line joining their centers of mass were determined. From Stark effect measurements, μa was redetermined and μc was shown to be nearly zero. Electrostatic calculations using distributed multipoles were carried out to explore the structure of this dimer.

The microwave spectrum, dipole moment and low frequency vibrational states for phosphabenzene

Abstract The microwave spectrum of the ground vibrational state and seven lowfrequency vibrational states for phosphabenzene (C5H5P) have been assigned. The small positive inertial defect and the alternation of intensities due to nuclear spin statistics for the ground state confirm a plannar structure with C2v symmetry. A PC bond distance of 1.70–1.73 A and 〈CPC of 101°–104° were estimated based on plausible assumptions for the other ring parameters. Four low-frequency fundamental modes of vibration were identified and vibrational assignments discussed. The nuclear spin statistics indicate that three of these modes were antisymmetric to the C2 axis while one mode was symmetric. The dipole moment has been determined as 1.54±0.02 D.

Microwave spectra of C2H4⋅H2O and isotopomers

The rotational spectrum of the ethylene‐water complex has been reexamined using Fourier‐transform microwave spectroscopy. Several new transitions were observed in the spectrum of the normal isotopic species. All the transitions were split into doublets with a 3:1 relative intensity ratio. Additionally, the spectra of C2H4⋅HDO, C2H4⋅D2O, C2H4⋅H218O, C2H4⋅H217O, cis‐CHD=CHD⋅H2O, trans‐CHD=CHD⋅H2O, 1,1‐CD2=CH2⋅H2O, and CHD=CH2⋅H2O were measured. Splitting patterns and relative intensities of the tunneling doublets of the isotopomers are consistent with a high‐barrier tunneling pathway which exchanges the two water hydrogen atoms. A second, low‐barrier internal rotation of the water about the hydrogen bond is proposed to explain anomalous dipole moment and 17O nuclear quadrupole coupling results.

Microwave Spectrum, Structure, and Dipole Moment of Difluorophosphine Borane

The structure of difluorophosphine borane (HF2P–BH3) has been determined from the microwave spectra of six isotopic species. The expected staggered conformation and Cs symmetry have been confirmed. The structural parameters are: d(PH) = 1.409 ± 0.004 A; d(PF) = 1.552 ± 0.006 A; d(PB) = 1.832 ± 0.009 A; d(BHa) = 1.226 ± 0.005 A; d(BHs) = 1.200 ± 0.007 A; ∠HaBHa = 112.7 ± 0.5°; ∠HaBHs = 115.9 ± 0.4°; ∠FPF = 100.0 ± 0.5°; ∠FPH = 98.62 ± 0.25°; ∠BPF = 117.7 ± 0.3°. Two angles (PBHs = 109.9 ± 0.3°; PBHa = 99.89 ± 0.26°) indicate a tilt of the borane group away from the fluorine atoms. The value of the dipole moment obtained from Stark splittings is 2.504 ± 0.030 D. A range for the barrier to internal rotation is estimated as 3600–4500 cal/mole. The change in structural parameters of HF2PBH3 compared to similar compounds, the stability of HF2PBH3 towards dissociation, and the tilted borane group are discussed.

Microwave spectrum, structure, barrier to internal rotation, dipole moment, and deuterium quadupole coupling constants of the ethylene-sulfur dioxide complex

The microwave spectra of the complex between ethylene and sulfur dioxide and nine of its isotopic species have been observed in a Fourier transform microwave spectrometer. The spectra exhibit a and c dipole selection rules; transitions of the normal species and several of the isotopically substituted species occur as tunneling doublets. The complex has a stacked structure with Cs symmetry; the C2H4 and SO2 moieties both straddle the mirror plane with the C2 axis of SO2 crossed at 90 ° to the carbon–carbon bond axis (i.e., only the S atom lies in the symmetry plane). The distance between the centers of mass (Rcm) of C2H4 and SO2 is 3.504(1) A and the deviation of their planes from perpendicular to Rcm is 21(2) ° and 12(2) °, respectively. The tunneling splittings arise from a rotation of the ethylene subunit in its molecular plane. The barrier to internal rotation is 30(2) cm−1. The dipole moment of the complex is 1.650(3)D. The deuterium nuclear quadrupole coupling constants for C2H3D⋅SO2 are χaa=−0.119(1) MHz, χbb=0.010(1) MHz, and χcc=0.109(1) MHz. The binding energy is estimated to be 490 cm−1 from the pseudo‐diatomic approximation. A distributed multipole electrostatic model is explored to rationalize the structure and binding energies.The microwave spectra of the complex between ethylene and sulfur dioxide and nine of its isotopic species have been observed in a Fourier transform microwave spectrometer. The spectra exhibit a and c dipole selection rules; transitions of the normal species and several of the isotopically substituted species occur as tunneling doublets. The complex has a stacked structure with Cs symmetry; the C2H4 and SO2 moieties both straddle the mirror plane with the C2 axis of SO2 crossed at 90 ° to the carbon–carbon bond axis (i.e., only the S atom lies in the symmetry plane). The distance between the centers of mass (Rcm) of C2H4 and SO2 is 3.504(1) A and the deviation of their planes from perpendicular to Rcm is 21(2) ° and 12(2) °, respectively. The tunneling splittings arise from a rotation of the ethylene subunit in its molecular plane. The barrier to internal rotation is 30(2) cm−1. The dipole moment of the complex is 1.650(3)D. The deuterium nuclear quadrupole coupling constants for C2H3D⋅SO2 are χaa=−0.119(1...

Microwave spectrum, structure, low frequency vibrations, dipole moment and quadrupole coupling constants of dinitrogen trioxide

The structure of N2O3 has been determined from the microwave spectrum of seven isotopic species. The detailed structure associated with the following planar configuration is: [graphic omitted] d(N2N3)= 1.864 A; d(N2O1)= 1.142 A; d(N3O4)= 1.202 A; d(N3O5)= 1.217 A; ∠O1N2N3= 105.1°∠O4N3N2= 112.7°∠O5N3N2= 117.5°. The torsional vibrational frequency has been measured as 124 ± 25 cm–1. The quadrupole coupling constants for the nitrosyl nitrogen are χaa=–2.34 MHz, χbb= 1.12 MHz, and χcc= 1.22 MHz. The dipole moment has been determined as |µa|= 2.05 D; |µb|= 0.54 D; and |µt|= 2.12 D inclined at an angle of 9.1° to the N—N bond. On the basis of these data, the bonding is discussed.

Microwave spectrum of benzene⋅SO2: Barrier to internal rotation, structure, and dipole moment

The microwave spectrum of the benzene⋅SO2 complex was observed with a pulsed beam Fourier‐transform microwave spectrometer. The spectrum was characteristic of an asymmetric‐top with a‐ and c‐dipole selection rules. In addition to the rigid‐rotor spectrum, many other transitions were observed. The existence of a rich spectrum arose from torsional–rotation interactions from nearly free internal rotation of benzene about its C6 axis. Transitions from torsional states up to m=±5 were observed. The principal‐axis method (PAM) internal rotation Hamiltonian with centrifugal distortion was used to assign the spectrum. Assuming six‐fold symmetry for the internal rotation potential, the barrier height was determined as V6=0.277(2) cm−1. The spectrum of C6D6⋅SO2 was also assigned. Analysis of the moments of inertia indicated that the complex has a stacked structure. The distance Rcm separating the centers of mass of benzene and SO2, as well as the tilt angles of the benzene and SO2 planes relative to Rcm were determ...

Fragmentative and stereochemical isomerization probes for homolytic carbon to phosphorus bond scission catalyzed by bacterial carbon-phosphorus lyase

Three bacterial strains, Agrobacterium radiobacter, Klebsiella oxytoca, and Kluyvera ascorbata, isolated by enrichment culture for carbon to phosphorus bond cleavage ability, were analyzed for the mode of C-P bond fission. The cleavage of alkyl phosphonic acids to alkanes and inorganic phosphates proceeded both aerobically and anaerobically, and growth on trideuteromethylphosphonic acid yielded trideuteromethane as product. These data indicate that functionalization of the organic moiety does not precede carbon to phosphorus bond cleavage. As probes for radical intermediates, cyclopropylmethylphosphonic acid and cis-1,2-dideutero-1-propenylphosphonic acid were used in growth experiments and the gaseous hydrocarbon products were examined. With the cyclopropylmethylphosphonic acid probe, all three bacteria produced methylcyclopropane, but only K. oxytoca and K. ascorbata also generated the acyclic olefin I-butene, and then only in very low quantity (0.6 and 0.3% versus methylcyclopropane, respectively). With the propenylphosphonic acid probe, cis-1,Zdideuteropropene was formed with greater than 98% retention of configuration with each bacterial strain. Only for K. oxytoca was the alternate product, in this case trans-1,2dideuteropropene, clearly detected at 1.5%. Thus, C-P bond fission may yield radical intermediates that are trapped efficiently at the enzyme active site or, alternatively, homolysis of the C-P bond may occur as a minor reaction pathway.