Randall R. Friedl

The rotational spectrum and structure of chlorine peroxide

The products of the ClO self‐reaction have been studied in a flowing chemical reactor using submillimeter wave spectroscopy. The complete spectrum between 415 to 435 GHz has been measured as well as selected transitions in the range 285 to 415 GHz. The major products have been identified as the ClO dimer (Cl2O2) and chlorine dioxide (OClO). The observed rotational b‐type spectra of the most abundant isotopic species35 ClOO35Cl and 37ClOO35Cl have been analyzed. The observed nuclear spin statistics for the main species, the relative abundance of the lesser species, and the structure determination demonstrate unambigiously that the ClO dimer must possess identical chlorine atoms in a peroxide structure. The rotational constants as well as a complete set of quartic centrifugal distortion constants have been determined. Structural parameters for the vibronic ground state have been calculated: rOO=142.59(21) pm, rClO=170.44(4) pm, ∠ClOO=110.07(1)° and dihedral angle=81.03(1)°. Rotational transitions in the fir...

Estimation of the reaction rate for the formation of CH3O from H + H2CO - Implications for chemistry in the solar system

It is argued that the formation of the methoxy radical (CH3O) from H + H2CO may play an essential role in the reduction of CO to CH4. The rate coefficient for this reaction has been estimated using the approximate theory of J. Troe (1977a, J. Chem. Phys. 66, 4745) and transition state theory. We briefly discuss the implications of this reaction for the chemistry of CO on Jupiter, in the solar nebula, for interpreting the laboratory experiments of A. Bar-Nun and A. Shaviv (1975, Icarus 24, 197) and A. Bar-Nun and S. Chang (1983, J. Geophys. Res. 88, 6662) and for organic synthesis in the prebiotic terrestrial atmosphere.

Kinetic isotopic fractionation and the origin of HDO and CH3D in the solar system

It is argued that photochemical processes, driven by ultraviolet starlight, could lead to large deuterium fractionation for H2O and CH4 relative to H2 in the primitive solar nebula. Implications for deuterium enrichment observed in planetary atmospheres are briefly discussed.

Interaction of peroxynitric acid with solid H2O ice

The uptake of peroxynitric acid (PNA), HO 2 NO 2 or HNO 4 , on solid H 2 O ice at 193 K (-80°C) was studied using a fast flow-mass spectrometric technique. An uptake coefficient of 0.15 ± 0.10 was measured, where the quoted uncertainty denotes 2 standard deviations. The uptake process did not result in the production of gas phase products. The composition of the condensed phase was investigated using programmed heating (3 K min -1 ) of the substrate coupled with mass spectrometric detection of desorbed species. Significant quantities of HNO 4 and HNO 3 desorbed from the substrates at temperatures above 225 K and 246 K, respectively. The desorbed HNO 3 , which was less than 9% of the desorbed HNO 4 and remained unchanged upon incubation of the substrate, was likely due to impurities in the HNO 4 samples rather than reaction of HNO 4 on the substrate. The onset temperatures for HNO 4 desorption increased with increasing H 2 O to HNO 4 ratios, indicating that HNO 4 , like HNO 3 , tends to be hydrated in the presence of water. These observations suggest possible mechanisms for removal of HNO 4 or repartitioning of total odd nitrogen species in the Earths upper troposphere and stratosphere.

Integrated band intensities of HO2NO2 at 220 K

Abstract Integrated intensities of the 803, 940, 1304, 1397, 1728, and 3540 cm-1 bands of peroxynitric acid (HO2NO2) have been measured at 220 K. Simultaneously-recorded u.v. (200–350 nm) and Fourier transform i.r. (700–4000 cm-1) spectra of low-pressure gas mixtures containing HO2NO2 predominantly were analyzed to determine the number densities of HO2NO2 in a multi-pass absorption cell within an error of approx. 10%. Absorption coefficients at 220 K in the strong 803 cm-1 band, which should be useful in the interpretation of atmospheric spectra containing spectral features of HO2NO2, are also reported at high-resolution (0.003 cm-1).

Measurement of the V–T energy transfer rates of highly excited 2A1 NO2

Production of electronic ground state NO2 (2A1) from 248 nm photolysis of HNO3 was detected by laser induced fluorescence (LIF). A growth in the LIF signal was observed following the photolysis and has been interpreted as the relaxation of NO2 through the higher vibrational levels of the X(2A1) state; an energy region where the probe laser photodissociates the NO2 instead of inducing fluorescence. The rate coefficients for NO2 relaxation through these high vibrational levels were determined by fits of time resolved LIF signal to a stepladder kinetic model. The results of the kinetic analysis suggest that the observed relaxation begins at the 2B2 threshold near 9500 cm−1 and extends downward through approximately 5 vibrational levels of the ground electronic surface. The derived quenching rate coefficients (in units of 10−12 cm3 molecule−1 s−1) are 0.51±0.05, 1.0±0.1, 1.4±0.2, 2.6±0.6, and 8.7±1.1 for Ar, He, N2, O2, and CO2 collision partners, respectively. The discrepancies between these coefficients and...

Absolute infrared band strength measurement of the ClO radical by Fourier transform infrared spectroscopy

Abstract High-resolution (0.005 cm −1 ) Fourier transform infrared (FTIR) spectra of the X 2 Π i - X 2 Π i (1-0) rovibrational bands of 35 Cl 16 O and 37 Cl 16 O were obtained in 1 Torr of helium carrier gas. ClO radicals were produced in a discharge-flow chemical reactor containing White-type optics. During acquisition of the FTIR spectra, a diode array spectrometer was used to monitor the ClO concentration by observing the A 2 Π i - X 2 Π i electronic band in the ultraviolet. After measuring the strengths of approximately 830 individual infrared lines from several spectra, a total band strength, S v = 13.1 ± 1.1 cm −2 atm −1 , and a first Herman-Wallis coefficient, α = (4.12 ± 0.62) × 10 −3 , were determined. The fundamental transition moment calculated from the band strength was −(3.9 ± 0.2) × 10 −2 D.

Kinetics and product studies of the reaction of Br, Cl, and NO with ClOOCl using discharge-flow mass spectrometry.

The kinetics of the reactions Cl + ClOOCl --> products, Br + ClOOCl --> products (7), and NO + ClOOCl --> products have been studied as a function of temperature at 1 Torr total pressure using a discharge-flow mass spectrometric technique. The measured rate coefficients, expressed in Arrhenius form, are k5 = (7.60 +/- 0.56) x 10(-11)exp((65.4 +/- 17.9)/T) cm3 s(-1) for 217 K < T < 298 K, and k7 = (5.88 +/- 0.50) x 10(-12) exp(-173 +/- 20/T) cm3 s(-1) for 223 K < T< 298 K. The observed temperature dependencies of these rate coefficients indicate a common direct halogen atom abstraction mechanism. Mass spectral product studies indicate that BrCl is the only major Br-containing product from reaction. Extensive product studies were used to estimate that the peroxide form of the ClO-dimer is formed in > 90% yield from the ClO self-reaction. No evidence for the formation of ClOClO and ClClO2 was observed. No reaction between NO and ClOOCl was observed and an upper limit of k8 < 1 x 10(-15) cm3 s(-1) for 220 K < T < 298 K was determined.

Kinetics of the OH + ClOOCl and OH + Cl2O Reactions: Experiment and Theory †

The rate coefficients for the reactions OH + ClOOCl --> HOCl + ClOO (eq 5) and OH + Cl2O --> HOCl + ClO (eq 6) were measured using a fast flow reactor coupled with molecular beam quadrupole mass spectrometry. OH was detected using resonance fluorescence at 309 nm. The measured Arrhenius expressions for these reactions are k5 = (6.0 +/- 3.5) x 10(-13) exp((670 +/- 230)/T) cm(3) molecule(-1) s(-1) and k6 = (5.1 +/- 1.5) x 10(-12) exp((100 +/- 92)/T) cm(3) molecule(-1) s(-1), respectively, where the uncertainties are reported at the 2sigma level. Investigation of the OH + ClOOCl potential energy surface using high level ab initio calculations indicates that the reaction occurs via a chlorine abstraction from ClOOCl by the OH radical. The lowest energy pathway is calculated to proceed through a weak ClOOCl-OH prereactive complex that is bound by 2.6 kcal mol(-1) and leads to ClOO and HOCl products. The transition state to product formation is calculated to be 0.59 kcal mol(-1) above the reactant energy level. Inclusion of the OH + ClOOCl rate data into an atmospheric model indicates that this reaction contributes more than 15% to ClOOCl loss during twilight conditions in the Arctic stratosphere. Reducing the rate of ClOOCl photolysis, as indicated by a recent re-examination of the ClOOCl UV absorption spectrum, increases the contribution of the OH + ClOOCl reaction to polar stratospheric loss of ClOOCl.

Kinetics of the HO2+BrO reaction overthe temperature range 233–348 K

The reaction BrO+HO 2 →products is the rate-limiting step in a key catalytic ozone destruction cycle in the lower stratosphere. In this study a discharge-flow reactor coupled with molecular beam mass spectrometry has been used to study the BrO+HO 2 reaction over the temperature range 233–348 K. Rate constants were measured under pseudo-first-order conditions in separate experiments with first HO 2 and then BrO in excess in an effort to identify possible complications in the reaction conditions. At 298 K, the rate constant was determined to be (1.73±0.61)×10 -11 cm 3 molecule -1 s -1 with HO 2 in excess and (2.05±0.64)×10 -11 cm 3 molecule -1 s -1 with BrO in excess. The combined results of the temperature-dependent experiments gave the following fit to the Arrhenius expression: k=(3.13±0.33)×10 -12 exp(536±206/T) where the quoted uncertainties represent two standard deviations. The reaction mechanism is discussed in light of recent ab initio results on the thermochemistry of isomers of possible reaction intermediates.