Jane K. Rice

Nonstatistical CO product distributions from the hot H‐atom reaction, H+CO2→OH+CO

The hot H‐atom reaction, H+CO2→OH+CO is investigated under several initial conditions designed to vary the angular momentum of the CO2 reactant. The translationally hot H atoms are produced by photodissociating H2S at 193 nm, resulting in a reaction exoergicity of ∼120 kJ mol−1. The internal energy in the CO product is monitored by laser‐induced fluorescence in the VUV spectral range. Under near‐nascent conditions we report the rotational distributions of CO in v‘=0 under CO2 reactant ‘‘temperatures’’ of 300, 70 and 40 K. Also reported are the rotational distributions of CO in v‘=1 at 300 K and 70 K and the population ratios of [v‘=1]/[v‘=0] at both initial CO2 temperatures. Three distinctively ‘‘dynamical’’ aspects of the potential energy (PE) surface are exhibited in this set of experiments: (i) As the CO2 reactant is cooled, a cooling of the CO distribution is seen which suggests the reaction intermediate does not live long enough to randomize its internal energy. (ii) We report a coupling of vibration...

Spectra, radiative lifetimes, and band oscillator strengths of the A 1Π–X 1Σ+ transition of BH

We report new spectroscopic information on the A 1Π–X 1Σ+ transition of BH including the observation of the 0–1 and 1–2 bands using laser induced fluorescence (LIF) techniques. Ratios of Einstein coefficients, band oscillator strengths and transition probabilities have been obtained for the 0–1 compared to the 0–0 band and the 1–0 and 1–2 compared to the 1–1 band. These ratios indicate that the emission observed occurs predominantly within the diagonal elements. Additionally, the radiative lifetimes of the v’=0, 1, and 2 levels have been measured to be 127±10, 146±12, and 172±14 ns, respectively. Using the ratios above and the experimental lifetimes, we have obtained Einstein emission coefficients and band absorption oscillator strengths. These values are compared to several calculations from the literature and in some instances large differences are seen.

The rotational and tunneling spectrum of the H2S⋅CO2 van der Waals complex

The rotational spectra of H2S⋅CO2 and two deuterated forms have been observed using a pulsed‐beam Fourier‐transform microwave spectrometer. For each of the three complexes we assign a‐type and c‐type transitions which are split into a ‘‘weak’’ and a ‘‘strong’’ intensity component. The analysis based on that previously used for the (H2O)2 complex and modified for application to H2S⋅CO2, allowed us to assign internal rotation, inversion tunneling states of the H2S and CO2 units in the complex. The following rotational constants were determined for the ground tunneling state of each species: for H2S⋅CO2, A=11 048.0(26) MHz, B=2147.786(4) MHz, and C=1806.468(4) MHz; for HDS⋅CO2, A=10 769(35) MHz, B=2107.26(24) MHz, and C=1775.83(24) MHz; and for D2S⋅CO2, A=10 356.2(28) MHz, B=2065.376(8) MHz, and C=1746.122(8) MHz. The electric dipole moments were determined for the H2S⋅CO2 and D2S⋅CO2 species, resulting in the values μa=0.410(14) D and μc=0.822(10) D for the H2S⋅CO2 species. The structure of the complex has ...

Non-statistical behavior in the rotational energy distribution of CO from the hot hydrogen atom reaction: H+CO2→OH+CO

Abstract The hot hydrogen atom reaction of H+CO 2 →OH+CO is examined under three different experimental conditions designed to assess the effect of the initial CO 2 angular momentum distribution on the CO product energy distribution. The CO product is monitored by laser-induced fluorescence in the VUV spectral region. The CO rotational distributions in ν″=0 are reported for CO 2 reactant “temperatures” of 300, 70 and 40 K. Preliminary results on the CO ν″=1 rotational population are also presented.

A search for subpicosecond absorption components in photosystem II reaction centers

Abstract The transient absorption kinetics of spinach photosystem II reaction centers were measured at 672 nm (detection bandwidth ≈ 11 nm) following excitation at 310 nm. A temporal resolution of ≈ 50 fs was used which is three times higher resolution than the current literature value. We observed a very fast absorption decrease with a rise time of 150 ± 15 fs followed by a 13 ± 4 ps recovery. The kinetics of the recovery step did not reveal a 3 ps component, however, a slight break in the data suggests a more complicated fit may explain the data as well or better. Based on a comparison of the rise time reported here and those reported by Durrant, the relaxation from S n to S 1 occurs very rapidly, within the 150 fs initial absorption decrease.

Selective catalytic activity toward hydrofluorocarbon refrigerants in mixed oxides of manganese and copper

Abstract We report selective activity of an oxidative catalyst made of manganese and copper oxides toward two ozone-safe refrigerants, HFC-236fa (CF3CH2CF3), and HFC-134a (CF3CFH2). These refrigerants are among those in a new class which contain hydrogen and fluorine substituents rather than fluorine and chlorine. This catalyst is generally non-specific and is used to oxidize carbon monoxide, hydrogen, and a variety of hydrocarbons and nitrogen compounds in heated burners, however, its activity toward refrigerants has been unpredictable. For our application, the catalyst is used in a heated burner in the closed-air environment on board submarines. In the process of optimizing the burner conditions for maximal activity toward airborne hydrocarbon contaminants and minimal activity toward refrigerants, we discovered enhanced and selective oxidative decomposition of these refrigerants in a group of recently-formulated catalyst lots which were manufactured with a higher percentage of ‘fines’. We attribute the increase in oxidative decomposition to an increase in adsorption of the refrigerants on the recently-formulated catalyst. We also observed some enhancement of activity toward CO on the recently-formulated catalyst. In addition to absorption isotherm measurements, we present several characterizations of the catalysts including scanning electron microscopy, elemental analysis, X-ray photoelectron spectroscopy, and temperature-programmed reduction.

Pulsed‐nozzle Fourier‐transform microwave investigation of the large‐amplitude motions in HBr–CO2

Microwave spectra of H79Br–CO2 and H81Br–CO2 and their D and 18O isotopomers have been measured using a pulsed‐nozzle Fourier‐transform microwave spectrometer. The spectra are consistent with a T‐shaped Br–CO2 geometry, as concluded previously by Zeng et al. [Y. P. Zeng, S. W. Sharpe, S. K. Shin, C. Wittig, and R. A. Beaudet, J. Chem. Phys. 97, 5392 (1992)] from an investigation of the rotationally resolved infrared spectrum of the asymmetric C=O stretching vibration of the complex. Only b‐type Ka=1←0 transitions are observed, with the symmetry‐allowed a‐type ΔKa=0 transitions being too weak to be detected. The absence of a strong a‐type spectrum implies that the HBr axis is nearly parallel to the b‐inertial axis of the complex, which itself is parallel to the C∞ axis of the CO2. The Ka=1←0 energy level spacing is approximately 1.2 GHz larger than that predicted from the infrared rotational constants due to an additional contribution to the splitting arising from the hindered‐rotation tunneling of the HBr...

Einstein transition probabilities for the AlH A 1Π—X 1Σ+ transition

Abstract Ratios of the Einstein transition probabilities, band oscillator strengths and vibrational transition probabilities for the (0,0) and (0,1) bands and the (1,0), (1,1), and (1,2) bands in the AlH A 1 Π—X 1 Σ + transition are measured. These ratios indicate that emission occurs predominantly in the diagonal terms. Using literature values of the lifetimes of the ν=0 and 1 levels, absolute Einstein transition probabilities are derived.

High-pressure matrix isolation of heterogeneous condensed phase chemical reactions under extreme conditions

Abstract A new technique which combines high-pressure and thermal-shock conditions with low-temperature matrix isolation in a gem anvil cell is presented. This serves to partially quench or arrest the reaction sequence of an energetic material. New chemical species are observed which indicate that intermediates are trapped in addition to final products. This combination of high pressure and low temperature helps elucidate the complicated reaction pathways in the deflagration to detonation regime. We have applied this technique to hexanitrohexaazaisowurtzitane (HNIW, chemical name: 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0 5,9 .0 3,11 ]dodecane). Products are identified using infrared spectroscopy and comparisons are made to previously reported data taken under thermal, ambient pressure conditions.

Theoretical and experimental investigation of the reaction BH+D2→BHD2

The rate of the association reaction, BH+D2→BHD2 is determined both theoretically and experimentally. In the theoretical calculations, potential‐energy surface information is obtained using multiconfiguration self‐consistent‐field and large‐scale multireference configuration‐interaction calculations with large correlation consistent basis sets. The preferred direction of approach is found to be along a non‐least‐motion pathway for which the BH and DD bonds come in nearly parallel to one another. The small computed activation energy of 2.6 kcal/mol for this highly exothermic reaction is found to arise almost exclusively from changes in zero‐point vibrational energy. The experimental measurements of the BH disappearance rate are made at temperatures from 298 to 597 K and are shown to be only weakly dependent on total pressure over the range of 1–100 Torr. As a test of the proposed mechanism, we observe the growth of BD and find the BD appearance rate constant to be in excellent agreement with that for BH disappearance. The measured reaction rates are compared to the results of canonical variational transition‐state theory calculations of the association rate and are found to be in excellent agreement.