S. H. Bauer

Spectroscopic Studies of the Hydrogen Bond. II. The Shift of the O–H Vibrational Frequency in the Formation of the Hydrogen Bond

The association spectra of a number of acids and alcohols in the region lambdalambda9000–11,000 have been observed both in solution and in the pure liquids. In each case a broad band with maximum near lambda10,000 was observed while in the alcohols an additional weaker band near lambda9000 appears to be present. Evidence is presented that the lambda10,000 band is to be identified with the O[Single Bond]H group. This evidence includes the behavior of the association band with change in concentration and temperature and its presence in several substances in which absorption other than that due to the O[Single Bond]H group is practically absent in the region studied. New evidence is given that a weak intermolecular hydrogen bond is formed between acetone and methyl alcohol. It is pointed out that the presence of absorption in the narrow O[Single Bond]H bands is not to be taken as evidence of the absence of hydrogen bonds in case the absorption is weak. The character of the O[Single Bond]H absorption in the case of intermolecular hydrogen bonds is discussed and the probable nature of the spectrum in the case of an intramolecular bond is indicated. A relation between the energy of the hydrogen bond and the shift of the O[Single Bond]H vibrational frequency is pointed out and its use is suggested in the interpretation of certain spectra.

Shock synthesis of amino acids in simulated primitive environments.

A mixture of gases roughly simulating the primitive terrestrial atmosphere has been subjected to shock heating followed by a rapid thermal quench. Under strictly homogeneous conditions there is a very high efficiency of 5 x 1010 molecules per erg of shock-injected energy for production of alpha-amino acids. Calculations suggest that rapid quenching bypasses the usual thermochemical barrier. The product of energy flux and efficiency implies the unexpected conclusion that shocks occurring on atmospheric entry of cometary meteors and micrometeorites and from thunder may have been the principal energy sources for pre-biological organic synthesis on the primitive earth.

Equilibrium Composition of the C/H System at Elevated Temperatures

Thermodynamic functions for a large number of C–H molecules were computed from the molecular parameters presented in the preceding paper. These functions and others taken from the literature were used to calculate the equilibrium composition of the C/H gas phase system over the composition range C/H=1/10, ¼, ½, 1, 2, 3. The temperature range was 500–5000°K, and the pressures used were 0.1, 1.0, and 10 atm. In additional calculations solid carbon was assumed to be present. Representative graphs of the results are presented. They show that the familiar, stable hydrocarbons are not important in characterizing the equilibrium composition above 2000°K. Acetylenic molecules and their radicals dominate the composition at high temperatures.

The early stages of pyrolysis and oxidation of methane

Abstract Measurement of post shock-front density-gradients generated by shock waves propagating through CH 4 Ar and CH4/O2/Ar mixtures provided data for estimating the rate constant for the primary dissociation step [CH4 + Ar → CH3 + H + Ar] in the bimolecular regime. A least-squares analysis of 24 runs covering the temperature range 1950–2770°K and total densities (2.37–8.91) × 10−6 mol cm−3 gave for k 1 (T) = 0.6 Z CH 4 M ( E 0 RT ) 4.2 exp ( (−E 0 RT) /4.2! cm 3 mol −1 s −1 , with E0 = 103.2 kcal/mole. The measured activation energy was 85.8 ± 1 kcal/mole. Within our experimental scatter the rate constant for CD4 was equal to that for CH4 but (possibly) with a slightly higher activation energy (+1.7 kcal). To fit the computed profiles of the density gradients to those observed, over particle times 0.5–50 μs, a 12-step mechanism was postulated and a reasonable set of rate constants derived. Our data combined with room temperature values for the termolecular association of CH3 with H atoms suggest that the association rate constant varies as ( 1 T )1.2. At CH 4 O 2 ratios 3.3 and 6.7, combustion is initiated when molecular oxygen is attacked by the primary products of pyrolysis. Ten additional steps are required to account for the recorded density gradient profiles. The sensitivity of the psfdg technique for imposing sharp criteria on proposed reactions that occur during the induction period of a combustion process is demonstrated in these studies. Comparisons were made between the 22-step mechanism derived in this investigation and a variety of mechanisms proposed in the literature.

The structures of acetylacetone, trifluoroacetyl-acetone and trifluoroacetone

Abstract The molecular geometries of three structurally related compounds have been determined by electron diffraction in the gas phase. Acetylacetone, which exists primarily as the enol tautomer, was found to have a planar symmetric ring with the following rg values: C1-C2 = 1.405± 0.005 A, C2-C4 = 1.510± 0.005 A, C-O = 1.287± 0.006 A, C-H = 1.090± 0.010 A, ∠C2C1C3 = 118.3 ± 1.8°, ∠C1C3O1 = 123.2± 1.7°, ∠C1C3C5 = 122.0± 1.2°, and ∠CCH = 110.2 ± 2.1°. A model in which the enol proton is in the ring plane located symmetrically between the oxygen atoms is in best agreement with the diffraction data. The structure of trifluoroacetylacetone is similar to that of acetylacetone. The rg values for this compound are C1-C3 = 1.4164 ± 0.006 A, C3-C5 = 1.511 ± 0.021 A, C2-C4 = 1.536 ± 0.018 A, C-O = 1.270 ± 0.008 A, C-H = 1.088 ± 0.039 A, C-F = 1.340 ± 0.005 A, ∠C2C1C3 = 117.2 ± 1.8°, ∠C1C2O2 = 123.6 ± 1.7°, ∠C1C3C5 = 118.1 ± 2.3°, ∠C1C2C4 = 123.0 ± 1.4°, ∠CCH = 109.0± 4.8°, and ∠CCF = 110.6± 0.8°. The rg values for the trifluoroacetone are: C1-C2 = 1.481 ± 0.019 A, C1-C3 = 1.562 ± 0.011 A, CO = 1.207 ± 0.006 A, C-H = 1.089 ± 0.024 A, C-F = 1.339 ± 0.003 A, ∠C2C1O = 122.0 ± 1.1°, ∠C3C1O = 116.8 ± 0.7 °, ∠CCH = 105.0 ± 2.2 °, and ∠CCF = 110.7 ± 0.3°. The significance of the error estimates is discussed briefly.

The absorption spectrum of BH and BD in the vacuum ultraviolet

The absorption spectrum of the BH radical has been obtained in the flash photolysis of borine carbonyl. Eleven new electronic transitions have been found which establish eight new electronic states and extend the available information on two others. Most of the upper electronic states are Rydberg states and, although no extended Rydberg series have been found, a value of the ionization potential of 9.77 ± 0.05 eV has been derived from them. Several of the excited states show the effects of strong l-uncoupling which is expected for Rydberg states but has been observed hitherto only for H2 and He2. The uncoupling effects in the 3p complex of BH are well represented by the formulas of Dieke and Weizel but for the 3d complex the corresponding formulas of Kovacs and Budo had to be modified since the zero rotation energies of Σ, Π, and Δ states are not proportional to Λ2 as required by these formulas. Values for the rotational and vibrational constants of most of the new electronic states have been derived and those for the known states have been improved. Corresponding data for BD have also been obtained. The observed isotope shifts between BH and BD in the B-X system can be made to fit the standard formulas only if an electronic isotope shift of 15·4 cm−1 is assumed.

Studies with a Single‐Pulse Shock Tube. I. The Cis—Trans Isomerization of Butene‐2

The cis—trans isomerization of butene‐2 was investigated behind reflected shocks in a single‐pulse shock tube of a novel design. The temperature range covered was 1000°—1250°K, and concentrations of 1% and 6% of the butene in argon were used. Analyses were made by vapor‐phase chromatography. The first‐order rate constants obtained in this work fall slightly above the extrapolated Arrhenius curves of two recent low‐temperature studies. An activation energy of 65, rather than 62.8 kcal/mole, is obtained when a straight line is drawn between the high and the low temperature data. |The rate constant obtained is kcis∞=3.5×1014exp(−65×103/RT). Possible sources of errors in evaluating reaction times in the single‐pulse shock tube are discussed.

Electron Diffraction Study of the Molecular Structures of Sulfur Tetrafluoride (SF4) and Thionyl Tetrafluoride (SOF4)

The molecular structures of SF4 and SOF4 in the gaseous state were determined by electron diffraction using sector‐microphotometer data. Both molecules were confirmed to have trigonal bipyramidal structures (C2v symmetry), with two nonequivalent sets of F–S bond distances. The bond lengths, in terms of the center of gravity parameter, rg, and the bond angles are as follows: For SF4:rg(equatorial S–F)=1.542±0.005 A,rg(polar S–F)=1.643±0.005 A,∠(equatorial F–S–F)=103.8∘±0.6∘,∠(polar F–S–F)=176.8∘±2.5∘.For SOF4:rg(equatorial S–F)=1.539±0.005 A,rg(polar S–F)=1.602±0.005 A,rg(S–O)=1.422±0.008 A,∠(equatorial F–S–F)=122.8∘±1.8∘,∠(polar F–S–F)=182.8∘±0.7∘.The polar F–S–F angles are measured along an arc which bisects the equatorial FSF angle.

Isotope Exchange Rates. III. The Homogeneous Four‐Center Reaction H2+D2

The homogeneous isotopic exchange reaction between hydrogen and deuterium in an excess of argon was studied in a 1‐in.‐diam single‐pulse shock tube. Reaction times behind the reflected shock were close to 1 msec and the temperature range was 1060°—1420°K. The hydrogen and deuterium were present in concentrations from 1%—10%, at total reaction densities of 1.18 to 5.31×10−2 mole/liter. Conversions were kept low in order to minimize the reverse reaction. From the average rates the reaction was found to be second order (total) and empirically represented by Δ[HD]/Δt=kp[Ar]0.98[D2]0.66[H2]0.38,kp=1012.84T12exp(−42 260/RT),cm3mole·sec−1.This power‐rate law, with the surprising asymmetry in the H2—D2 dependence, can be rationalized by assuming that exchange occurs with high probability only during encounters between H2—D2 pairs, one of which is vibrationally excited to approximately 30 kcal/mole; that the probability for metathesis is low between molecules in their low‐lying vibrational states even when their relative kinetic energy along the line of centers plus vibrational excitation exceeds the activation energy. Support for this mechanism is provided by an approximate calculation of the pre‐exponential term of the exchange rate constant from vibrational relaxation data.The homogeneous isotopic exchange reaction between hydrogen and deuterium in an excess of argon was studied in a 1‐in.‐diam single‐pulse shock tube. Reaction times behind the reflected shock were close to 1 msec and the temperature range was 1060°—1420°K. The hydrogen and deuterium were present in concentrations from 1%—10%, at total reaction densities of 1.18 to 5.31×10−2 mole/liter. Conversions were kept low in order to minimize the reverse reaction. From the average rates the reaction was found to be second order (total) and empirically represented by Δ[HD]/Δt=kp[Ar]0.98[D2]0.66[H2]0.38,kp=1012.84T12exp(−42 260/RT),cm3mole·sec−1.This power‐rate law, with the surprising asymmetry in the H2—D2 dependence, can be rationalized by assuming that exchange occurs with high probability only during encounters between H2—D2 pairs, one of which is vibrationally excited to approximately 30 kcal/mole; that the probability for metathesis is low between molecules in their low‐lying vibrational states even when their r...

Bimolecular Reaction of N2O with CO and the Recombination of O and CO as Studied in a Single‐Pulse Shock Tube

The reaction between N2O and CO was studied in a single‐plus shock tube over the temperature range 1320°–2280°K, in mixtures of the reactants highly diluted with Ar. In the range of temperatures 1317°–1908°K the rate constant for the bimolecular reaction, N2O+CO→ lim 1N2+CO2, was found to be k1 = 1.1 × 1011exp(− 23 000 / RT) cm3mole−1·sec−1. From the rates of formation of CO2 above 1642°K, a constant for the nonradiative third‐order recombination of O and CO was obtained (for the temperature range 1500°–3000°K), O+CO+Ar5→ lim 5CO2+Ar, k5 = 2.8 × 1012exp(+ 23 800 / RT) cm6mole−2·sec−1. The large negative activation energy so deduced is shown to be in full agreement with the low value for the activation energy previously observed for CO2 decomposition. An energy diagram was constructed on the basis of a recent CO flame study and results on the limiting high‐pressure CO2 decomposition. The mechanisms for the radiative and the three‐body recombination, and the dissociation of CO2, are discussed in terms of th...