Ab initio molecular orbital calculations on the structure and stability of the nitrate and sulfate and sulfate complexes of uranyl (UO22+) and plutonyl (PuO22+) using effective core potentials are reported. It is found that the binding energy of sulfate is greater than that of nitrate to both uranyl and plutonyl, with a slight preference for plutonyl. A method of decomposing the binding energy into electrostatic, Pauli repulsion, polarization and charge-transfer components is described which predicts that electrostatic forces are dominant. A simple molecular mechanics potential is developed by using this finding, which is successful in reproducing the ab initio results.

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Millimetre-wave rotational spectra have been recorded for the molecules (CH3)(3CBr)-Br-79, (CH3)(3CBr)-Br-81 and (CH3)(3CI)-I-127. In addition, we have recorded low-J spectra at much greater precision using a Fourier-transform spectrometer. The combined results yield rotational, centrifugal distortion, quadrupole and spin-rotation constants which are more accurate than any determined independently.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Ground state rotational spectra of the three isotopomers (CH2)2O...H35Cl, (CH2)2O...H37Cl, and (CH2)2O...D35Cl of a short-lived hydrogen-bonded dimer have been detected in the reactive mixture of oxirane and hydrogen chloride by using a fast-mixing nozzle in conjunction with a Balle–Flygare Fourier-transform microwave spectrometer. Rotational constants, centrifugal distortion constants and Cl-nuclear quadrupole coupling constants were determined for each isotopomer. In particular, all four components χaa, χbb, χcc, and χac of the coupling tensor were obtained. A detailed analysis of the rotational constants allows the conclusion that the dimer has Cs symmetry, with a steeply pyramidal arrangement completed at oxygen by the hydrogen bond with HCl. Diagonalization of the complete Cl-nuclear quadrupole coupling tensor leads to the principal axis components χxx, χyy, and χzz (where z is the HCl direction in the dimer). The angle of rotation α is the angle between the HCl (z) direction and the a-axis direction in the equilibrium conformation of the dimer. It is larger by ∼10° than the angle γ between the O...Cl internuclear line and the principal inertial axis a in each case and implies that the hydrogen bond is bent by 180-θ=∼16.5° from the collinear arrangement O...H–Cl (θ=0). The angle 180-θ and the angle φ=76.2° made by the O...Cl internuclear line with the extension of the oxirane local C2 axis are interpreted in terms of a simple model of the hydrogen bond.

Ground-state rotational spectra of the isotopomers C2H6…HC14N and C2H6…DC14N of a weakly bound dimer formed by ethane and hydrogen cyanide have been analysed to give the spectroscopic constants B0, DJ, DJK and χ(14N) in each case. The dimer is shown to have a C3v equilibrium geometry, with HCN lying along the molecular symmetry axis and its H atom forming a hydrogen bond to a terminal face of a methyl group of ethane. The propensity of a CH3 group to act as a proton acceptor in hydrogen bond formation is discussed.

The rotational spectra of the two isotopomers (CH4, H79Br) and (CH4, H81Br) of a weakly bound dimer formed between methane and hydrogen bromide have been observed by pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectra are of the symmetric-top type, but with the K=0 transition exhibiting a vibrational satellite. Observed spectroscopic constants are interpreted in terms of a C3v equilibrium geometry in which HBr forms a hydrogen bond to one of the four equivalent faces of the methane tetrahedron and lies along one of the methane C3 axes. The vibrational satellite is associated with internal rotation of the CH4 subunit which exchanges the site of hydrogen-bonding between the four methane faces.

The rotational spectra of the isotopomers CH4...(HCN)-N-14, (CH4)-C-13...(HCN)-N-14, CH4...(DCN)-N-14, CH4...(HCN)-N-15, CH4...(DCN)-N-15, CH3D...(HCN)-N-14 and CH3D...(HCN)-N-15 of a weakly bound dimer formed between methane and hydrogen cyanide have been observed by pulsed-nozzle, Fourier-transform microwave spectroscopy. Each dimer species containing a T(d) methane isotopomer exhibits a symmetric-top type spectrum consisting of two K = 0 transitions and two K = 1 transitions. The spectrum in each of the four states has been analysed to give an operationally defined rotational constant B and centrifugal distortion constant D(J), as well as N-14 and/or D nuclear quadrupole coupling constants, as appropriate. For the species CH3D...(HCN)-N-14 and CH3D...(HCN)-N-15, spectra in three K = 0 states were observed and similarly analysed. These observations have been interpreted in terms of a C3v equilibrium geometry of the dimer in which HCN lies along a C3 axis of methane and forms a hydrogen bond to one of the four equivalent faces of the methane tetrahedron. The observed spectral patterns are discussed on the basis of the internal rotation of the methane subunit which permutes the site of weak binding among the faces of the tetrahedron, especially with reference to the correlation diagram (due to Ohshima and Endo, J. Chem. Phys., 1990, 93, 6256) linking the free rotor states of methane in the low-barrier limit with the K states in the rigid C3v geometry limit. The distance r(C...C) = 3.837 (3) angstrom between the C atoms of CH4 and HCN is remarkably insensitive either to variation of the internal rotation state or the nature of the isotopomer. The same conclusion holds for the intermolecular stretching force constant which has the value k(sigma) = 1.60 (2) N m-1 for isotopomers containing HCN.

The nuclear quadrupole coupling constants χ(79Br) and χ(81Br) have been determined for the ground state of 1-bromoadamantane by pulsed-nozzle, Fourier-transform microwave spectroscopy. A comparison of similar coupling constants for the series methyl bromide, ethyl bromide, t-butyl bromide and 1-bromoadamantane shows that the ionic character of the CBr bond increases along this series.

A hydrogen-bonded dimer formed by thiirane with hydrogen bromide has been detected and characterized in the gas phase by means of its ground-state rotational spectrum. The spectrum was detected within ca. 1-mu-s of the creation of the nascent dimer by using a fast mixing nozzle in conjunction with a pulsed-nozzle, FT microwave spectrometer. With the former device the reactive components thiirane and hydrogen bromide remain separate until they expand into the Fabry-Perot cavity of the latter. Rotational constants A(o), B(o) and C(o), centrifugal distortion constants DELTA-J, DELTA-JK and delta-J, Br nuclear quadrupole coupling constants chi-aa, chi-bb and chi-ab, and Br spin-rotation coupling constants have been determined for each of the isotopomers (CH2)2S...(HBr)-Br-79 and (CH2)2S...(HBr)-Br-81. Interpretation of the various spectroscopic constants leads to the conclusion that the dimer has C(s) symmetry, with HBr lying in the plane perpendicular to the thiirane heavy-atom plane and with a pyramidal arrangement at S. There is some evidence of a bent hydrogen bond. The angle phi almost-equal-to 80-degrees made by the S...H line with the thiirane plane is discussed in terms of some simple rules for predicting angular geometries of hydrogen-bonded dimers and a non-bonding electron-pair model for thiirane.

The rotational spectrum of the dinitrogen-acetylene dimer has been obserbed by pulsed-nozzle, Fourier-transform microwave spectroscopy. The 14N nuclear quadrupole coupling constants have been corrected for the effects of the angular oscillation of the N2 subunit in the zero-point state of the dimer and for the electrical effect of the nearby acetylene subunit. The corrected quantity −5.01(13) MHz thus provides an essentially experimental value of the coupling constant of the free dinitrogen molecule.

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The ground-state rotational spectra of ten isotopomers of the carbon monoxide—acetylene dimer are reported and the spectroscopic constants BO and DJ determined in the usual way in a semirigid rotor fit for a linear molecule. The BO values are consistent with a simple linear model of the dimer with nuclei in the order OC…HCCH. The failure to observe the isotopomer OC…HCCD in mixtures of CO and HCCD is interpreted in terms of a zero-point energy difference rather than in terms of a nearly free internal rotation of the acetylene subunit.

Ground-state rotational transitions allowed by the component μc of the electric dipole moment in the dimer (CH2)2O…HF have been measured and lead to improved rotational constants. The absence of inversion doubling in these transitions allows a lower limit to be placed on the barrier to inversion of the configuration at oxygen. The magnitude of the determined H, F spin—spin coupling constant suggests that the O…H—F system may be non-linear.

The ground-state rotational spectra of three symmetric-top isotopomers (CH3)3 14N⋅⋅⋅H 79Br, (CH3)3 14N⋅⋅⋅H 81Br, and (CH3)3 14N⋅⋅⋅D 79Br of the heterodimer of trimethylamine and hydrogen bromide have been detected by pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectroscopic constants B0, DJ, DJK, χ(14N), and χ(Br) have been determined for each of the isotopomers and for (CH3)3 14N⋅⋅⋅H 81Br have the values 1161.6294(2) MHz, 0.148(5) kHz, 7.77(2) kHz, −2.883(7) MHz, and 99.645(7) MHz, respectively. A comparison of the 14N– and 81 Br–nuclear-quadrupole coupling constants χ(14N) and χ(Br) with those expected on the basis of a hydrogen-bonded model (CH3)3N⋅⋅⋅HBr and an ion-pair model (CH3)3NH+⋅⋅⋅Br− leads to the conclusion that in the heterodimer trimethylamine-hydrogen bromide there is a significant extent of proton transfer from HBr to (CH3)3N. The value of the intermolecular stretching force constant kσ=82(3) N m−1 determined from DJ is also compared with those expected for the limiting models of the dimer and is found to lie close to that associated with the ion-pair limit.

The rotational spectra of the two isotopomers (CH2)2O...H79Br and (CH2)2)...H81Br of a dimer formed between oxirane and hydrogen bomide have been detected with a pulsed-nozzle, Fourier-transform microwave spectrometer. A fast mixing nozzle was used to form and then isolate the observed species before the rapid ring-opening reaction could occur. Rotational constants, centrifugal distortion constants, and Br nuclear hyperfine (quadrupole and spin-rotation) coupling constants were determined. The following constants in particular were used to diagnose the nature of the observed species:[GRAPHICS]A detailed analysis of the observed rotational constants allows the conclusion that the dimer has C(s) symmetry with a pyramidal arrangement at oxygen and an oxirane geometry essentially unperturbed on dimer formation. When H of HBr is assumed to lie between O and Br the distance r(O...Br) = 3.2623 (12) angstrom and the angle theta = 78.45 (9)-degrees are determined. Diagonalization of the complete Br nuclear quadrupole coupling tensor leads to Xzz = -202.457 MHz and Xyy = 205.527 MHz, indicating that the presence of the oxirane molecule only slightly perturbs the cylindrical symmetry of the HBr subunit. The angle of rotation of (alpha-za)x = 23.3-degrees required to diagonalize the x tensor is ca. 10-degrees larger than the angle (alpha-za)struct implied by the determined geometry. This suggests that the angle O...H-Br might be correspondingly less than 180-degrees, i.e. the hydrogen bond might be slightly bent.

The rotational spectra of five isotopomers of the dimer (CH4,HCl) and two isotopomers of the dimer (CH4,HF) have been investigated by the pulsed-nozzle FT microwave technique. Detailed consideration of the spectroscopic constants allows the conclusion that the HCl complex has an effective C3ν geometry of the type CH4…HCl with a single hydrogen bond and internal rotation of the CH4 subunit while the interaction in (CH4,HF) is of the two-centre type, involving bonds CH…F and C…HF, which appears effectively to quench the internal rotation.

Spectroscopic constants determined from the ground-state rotational spectrum of a weakly bound dimer formed between methane and hydrogen cyanide are interpreted to yield the surprising result that the dimer geometry is of C3v symmetry, but with the HCN molecule acting as the proton donor and CH4 as the proton acceptor, i.e. CH4⋯ HCN.

The spectral simplification that accompanies the very low effective temperatures achieved in a pulsed-nozzle, Fourier-transform microwave spectrometer has been used to advantage to observe the ground-state rotational spectra of the singly substituted isotopomers (CH3)3CN13C, (CH3)3C15NC, (CH3)313CNC and (13CH3) (CH3)2CNC in their natural abundance in a sample of t-butyl isocyanide. The small linewidths characteristic of the technique have allowed the 14N-nuclear-quadrupole hyperfine structure to be resolved in the observed transitions of these isotopomers as well as in those of the most abundant species. Values of the 14N-nuclear-quadrupole coupling constants, the rotational constants and the centrifugal distortion constants for the isotopomers investigated are reported. After correcting the observed rotational constants for the small shrinkages of bonds that accompany the isotopic substitutions, the following rs geometry of the heavy-atom skeleton of t-butyl isocyanide was determined: r(NC1 = 1.1674(14) Å, r(C2N) = 1.454 (15) Å, r(C3,4,5C2) = 1.531 (4) Å, ∠ C3C2C4 = 111.2 (5) ° and ∠ C3,4,5C2N = 107.6 (5) °.

ChemInformVolume 20, Issue 40 Physical Organic Chemistry ChemInform Abstract: Ground-State Rotational Spectrum of tert.-Butyl Isocyanide and an rs Geometry of Its Heavy-Atom Skeleton. N. W. HOWARD, N. W. HOWARD Dep. Chem., Univ. Exeter, Exeter, Devon EX4 4QD, UKSearch for more papers by this authorA. C. LEGON, A. C. LEGON Dep. Chem., Univ. Exeter, Exeter, Devon EX4 4QD, UKSearch for more papers by this authorC. A. REGO, C. A. REGO Dep. Chem., Univ. Exeter, Exeter, Devon EX4 4QD, UKSearch for more papers by this authorA. L. WALLWORK, A. L. WALLWORK Dep. Chem., Univ. Exeter, Exeter, Devon EX4 4QD, UKSearch for more papers by this author N. W. HOWARD, N. W. HOWARD Dep. Chem., Univ. Exeter, Exeter, Devon EX4 4QD, UKSearch for more papers by this authorA. C. LEGON, A. C. LEGON Dep. Chem., Univ. Exeter, Exeter, Devon EX4 4QD, UKSearch for more papers by this authorC. A. REGO, C. A. REGO Dep. Chem., Univ. Exeter, Exeter, Devon EX4 4QD, UKSearch for more papers by this authorA. L. WALLWORK, A. L. WALLWORK Dep. Chem., Univ. Exeter, Exeter, Devon EX4 4QD, UKSearch for more papers by this author First published: October 3, 1989 https://doi.org/10.1002/chin.198940044AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume20, Issue40October 3, 1989 RelatedInformation