The association spectra of a number of acids and alcohols in the region λλ9000–11,000 have been observed both in solution and in the pure liquids. In each case a broad band with maximum near λ10,000 was observed while in the alcohols an additional weaker band near λ9000 appears to be present. Evidence is presented that the λ10,000 band is to be identified with the O–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–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–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–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–H vibrational frequency is pointed out and its use is suggested in the interpretation of certain spectra.

No abstract

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 10(10) 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.

The decomposition of nitromethane was studied over the temperature range 1000−1100 K in reflected shock waves. CH3NO2 and the reaction products were analyzed by gas chromatography. The derived gross rate constant and activation energy for the disappearance of CH3NO2 is consistent with that of Glänzer and Troe. A reaction mechanism consisting of 99 chemical reactions was developed to simulate the experimental data of the present study and that of Hsu and Lin. Good agreement between experiments and simulations was achieved. It appears that significant amounts of CH3NO2 are destroyed through secondary reactions that involved highly reactive free radicals (H, OH, and CH3), suggesting the need for redeterming the true unimolecular decay rate constant for CH3NO2. For improvement of the performance of the model, several other rate constants also need to be determined. The final section is a preliminary report on a spectrophotometric technique for measuring the loss of nitromethane due to pyrolysis by recording its absorption of UV radiation, directed axially along a small diameter shock tube. Although only semiquantitative data were obtained, this novel procedure merits discussion.

No abstract

No abstract

No abstract

The large absorption cross sections for infrared radiation possessed by a few rather stable molecular species, their relatively fast vibration-translation relaxation times, and the availability of large laser fluxes at their characteristic frequencies have been effectively exploited to generate high bath temperatures for gas-phase reactions under strictly homogeneous conditions. Controlled temperatures from 500 to 1500°K have been developed with ii modest COs laser. Rise times for heating are estimated to be in the millisecond range, with reaction times = 10 seconds. Operating pressures [reagents, radiation absorber (generally SFe,), and diluent] range from 10 to 100 torr. Thus laser-powered homogeneous pyrolysis (LPHP) is complementary to the single-pulse shock-tube technique [rise time -10-8 sec; reaction time sec] for obtaining product distributions in gas-phase pyrolvses, and for measuring relative rates in the absence of hot walls. The latter may (and generally do) introduce catalytic effects. Further, LPHP is very simple and ideally suited for exploratory investigations of small amounts of reagent ( mole); also, sample cells may be heated externally to augment the vapor pressure of slightly volatile reagents. Conventional analytical procedures (gas chromatography, mass spectrometry) were used to follow the course of pyrolysis.The primary chemical kinetic parameters, the temperature and density of the reactants, have both spatial and temporal distributions. Computer programs were developed for estimating T ( r , x ; t ) , given the radial intensity distributon in the incident beam, the absorption coefficient of the SF6 (as a function of density and temperature) for the irradiating line, as well as the mean heat capacity and thermal conductivity of the gas mixture. However, the computed profiles did not prove useful since the effects of convection, which could not be included in the calculations, perturb the initial distribution significantly within a few milliseconds. Indeed, it proved practical to enhance convection so as to homogenize the cell composition. When the incident radiation was chopped, frequencies ranging from 100 Hz to 1 Hz gave the same product distributions. A practical procedure is to use a "chemical thermometer" to establish a mean effective temperature for a given experimental configuration. Examples showing how to measure relative rate constants for molecular conversions, and the use of LPHP for qualitative determinations of product distributions as a function of temperature are presented. Finally, a number of hightemperature conversions are described to illustrate the utility of LPHP for flash thermolysis.