Fourier transform method for collision dynamics: Model studies of one-dimensional double well and anharmonic potentials

The method described in the accompanying paper is applied to several one-dimensional model systems, separated into simpler subsystems by arbitrary reflection barriers. The examples include an asymmetrical potential well, arbitrarily subdivided, a symmetrical double well, and a gaussian potential barrier. A true second-order iterative process is used.     

Different properties of exciplexes and excited states of CT complexes in the solid phase

The fluorescence, excitation and absorption spectra and fluorescence decay kinetics of charge-transfer (CT) complexes and exciplexes ofheteroaromatic cations and some other electron acceptors were investigated in ethanol at 77 K. Experimental data indicate that the fluorescence state of the exciplex may differ from that of the CT complex.     

Transient ESR nutation signals in excited aromatic triplet states

Transient ESR nutation signals following laser pulse excitation are analyzed for the case of the photoexcited triplet state of acridine in a molecular crystal matrix. Essential features, in particular the short rise-time (< 10^?7) of the signals, can be related to the inhomogeneous nature of the ESR linewidth. Applications are discussed.     

Protonation of metal carbonyl complexes : VI. Protonation of manganese π-cyclopentadienylphosphine complexes studied by 13C and 31P NMR techniques

¹³C and ³¹P NMR techniques have been applied to the complexes CpMn(CO)L₂ and CpMn(CO)₂ L (where L₂ is a bidentate tertiary phosphine, L is a monodentate tertiary phosphine, and Cp is cyclopentadienyl). It is shown that the complexes are protonated reversibly, when dissolved in CH₂Cl₂ in the presence of CF₃COOH, with the proton attacking the manganese atom.     

The zero point average structure of isobutane as determined by electron diffraction and microwave spectroscopy

The molecular structure of isobutane in the gas phase was investigated by combining electron diffraction data with microwave spectroscopic rotational constants of Lide.The analysis indicated that the tertiary C-H distance (r_g = 1.122±0.006 Å) was substantially longer than the average methyl C-H distance (r_g = 1.113±0.002 Å). Other structural parameters obtained were: r_g(C-C) = 1.535±0.001 Å, ∠CCC = 110.8±0.2°, and the average ∠CCH (methyl) = 111.4±0.2°.     

Effect of quadratic interactions on the resonance raman scattering of T × t2 jahn-teller systems

Raman excitation profiles and depolarization dispersion curves are calculated for T × t₂ Jahn-Teller systems that are subject to quadratic vibronic (Renner-Teller) coupling as well as frequency changes of the active vibrational mode.     

Electrolyte—formamide interactions studied by raman spectroscopy

The effects of dissolved electrolytes on the structure of liquid formamide have been investigated by Raman spectroscopy. The spectral features are dependent on the concentration and nature of the dissolved electrolyte and are discussed in terms of direct electrolyte formamide interactions. Two vN—H bands, arising from ion—formamide species, have been observed superimposed on the spectrum of residual liquid formamide. The results lend further support to the interaction model for electrolytes in liquid formamide previously proposed by us on the basis of nuclear magnetic resonance and infrared spectral data.     

Distortion of the triplet state of benzene in a borazole host. A study by microwave induced delayed phosphorescence at 1.2 K

The zero-field splitting parameters of C₆H₆ and C₆D₆ in a borazole crystal host have been measured. The absolute value of the parameter E is three times as large as for C₆H₆ in C₆D₆. The relative rate constants for radiative decay in some vibronic bands have been obtained by MIDP methods. In the OO band of the phsophorescence spectrum the radiation stems from the upper zf level indicating a quinoid electronic structure for benzene in borazole, i.e. opposite to that for C₆H₆ in C₆D₆.     

Cationic di- and mono-carbonyl complexes of manganese(I)

The complexes fac-O₃ClOMn(CO)₃(NN) (NN = 1,10-phenantroline (phen) or 2,2'bipyridine (bipy)) react with an excess of the ligands L [L = P(OR)₃ or P(OR)₂Ph, R = Me or Et] in refluxing ethanol to give cis-trans-[Mn(CO)₂-(NN)L₂]ClO₄, or the more highly substituted [Mn(CO)(NN)L₃]ClO₄ if the reaction is carried out under UV irradiation. Carbonylation at normal pressure of the latter complexes results in the formation of cis-cis-[Mn(CO)₂(NN)L₂]ClO₄, which undergo isomerization to the cis-trans isomer when heated in acetone.Treatment of fac-O₃ClOMn(CO)₃(dpe) (dpe = 1,2-bis(diphenylphosphino)-ethane] with bipy or phen in refluxing ethanol gives the corresponding cis-[Mn(CO)₂(NN)(dpe)]ClO₄ complexes, and irradiation of these with UV in the presence of an excess of P(OR)₃ (R = Ph, Et or Me) gives the monocarbonyls [Mn(CO)(NN)(dpe)L]ClO₄.     

Preparation and aluminum trichloride-induced cationic rearrangements of bicyclo[2.2.0]hexene carboxylic esters

Reaction between the tetramethyl[4]annulene aluminum trichloride σ-complex and α, β-alkenic esters gave the corresponding 1,4,5,6-tetramethylbicyclo[2.2.0]hex-5-one-2-endo-carboxylic esters. AlCl₃-induced cationic rearrangements of these bicyclic esters yielded a number of bicyclo[3.1.0]hexene carboxylic esters and related lactones which were isolated and identified. The isomerization seems to proceed via stereospecific endo protonation and subsequent rearrangement to 2-methoxycarbonyl-1,4,5,6-exo-tetramethylbicyclo(3.1.0]hex-4-yl carbocations.     

Charge-transfer properties of the hydrogen bond: Part 6. Charge-transfer theory and dipole moments of hydrogen-bonded complexes

The enhancement of the dipole moments of hydrogen-bonded complexes are discussed using Mulliken's charge-transfer theory.A linear relation is found between the ratio a/b and the ionization potential of the donor, I^V_D. This behaviour is similar to that previously found for halogen charge-transfer complexes [6].     

Vibrational studies in aqueous solutions: Part II. The acid oxalate ion and oxalic acid

Assignments for oxalic acid in solution are re-examined. A detailed assignment of the IR and Raman spectra of the acid oxalate ion is presented for the first time. Raman spectroscopy is used to study the first ionization of oxalic acid.     

Geometry optimization of the ring-opened oxirane diradical: mechanism of the addition reaction of the triplet oxygen atom to olefins

Geometry optimizations of several low-lying diradical states of the ring-opened oxirane (·CH₂CH₂O·) were performed by using the energy gradients of the UHF MINDO/3, STO-3G and 4-31G solutions. Both the STO-3G and 4-3 IG methods predict that the most stable form is the triplet state of the non-twisted σπ conformation in which the unpaired spins localized on the terminal carbon and oxygen atoms are oriented perpendicularly to each other. The singlet σσ diradical state in which both the radical-site p orbitals are coplanar with the molecular framework is only 2.3 (STO-3G) and 1.2 (4-31G) kcal/mol less stable than the triplet σπ diradical state. It is found that the geometry of the singlet σσ diradical is unique in that the C-C-O angle is noticeably small as compared with various other diradical states. Implications of these results to the mechanism of the oxirane-forming O(³P) + C₂H₄ reaction are discussed.     

Vibrational studies in aqueous solutions: Part I. The oxalate ion

The assignment of the fundamental modes and the symmetry of the oxalate ion in solution are re-examined in the light of new experimental evidence. Particular attention is given to the Raman bands at 1455 and 1488 cm^?.     

Properties of strong hydrogen-bonded systems: The formation of hydrogen-bonded ion pair in amine·HCL systems

The hydrogen-bonded complexes between CH₃NH₂ and (CH₃)₂NH with HCl have been studied by the ab initio molecular orbital method using the 4–31G basis set. Calculations show that the proton potential curve has a single minimum near to the nitrogen atom in both complexes. This means that the proton has been transferred from HCl to the amine. ΔE and the dipole moment of the complexes studied are as follows: ?18.2 kcal mol^?1, 10.3 D for methylamine ·HCl, and ?21.7 kcal mol^?1 11.1 D for the corresponding dimethylamine complex. Other properties of the hydrogen-bonded ion pairs are discussed.     

On the nature of excited electronic states in cyanine dyes: implications for visual pigment spectra

CNDO/S CI calculations are carried out on polyenes and on cyanine dyes. In contrast to polyenes, doubly excited configurations have a strong effect on the first optically allowed excited state in cyanines. Protonated Schiff bases of retinal are closely related to cyanine dyes, with important consequences for models of visual pigment spectra and photochemistry.     

Pavoninins,shark-repelling and ichthyotoxic steroid n-acetylglucosaminides from the defense secretion of the sole pardachirus pavoninus (soleidae)

Six steroid itN-acctylglueosaminides, pavoninins-1 to -6, have been isolated from the defense secretion of the sole P. pavoninus guided by ichthyotoxicity and hemolytic activity, and their structures determined to be 1–6 by spcctroscopic studies and chemical correlations. The pavoninins are considered to be the factors responsible for the repellent property of the sole against predatory fishes.     

The crystal structure of bicyclo [3.3.3]undecane-1,5-diol and the conformation of bicyclo[3.3.3]undecane (manxane)

The crystal structure of bicyclo [3.3.3]undecane-1,5-diol has been determined. It is monoclinic, P2₁/c, a = 12.99(2), b = 14.16(2), c = 12.50(1)A,β = 112.42(2)°, with two independent molecules in the asymmetric unit. One of these is disordered, but the other has almost exact C_3h symmetry and its conformation and precise molecular geometry agree well with previous calculations by molecular mechanics. The molecule shows considerable angle strain, having bridge angles in the range 118–121°     

The polar properties of valence bonds

Arguments based on bond-stretching frequencies, nuclear quadrupole coupling constants and bond lengths indicate that bonds having the same strength factor can have different electronic structures. It is then argued that a more useful probe for obtaining an insight into bond character is provided by infrared band intensities which can be analyzed to yield values for the constants occurring in bond moment functions. A new bond moment theory, in which the concept of “rehybridization moments” is introduced, is described. Using this theory, self-consistent values are obtained for the bond moment constants governing the band intensities for the molecules HCN, C₆H₆ and C₂H₄.