OH Reactivity and UV Spectra of Propane, n-Propyl Bromide, and Isopropyl Bromide

Evidence for lactone formation during infrared multiple photon dissociation spectroscopy of bromoalkanoate doped salt clusters

Reaction mechanisms of organic molecules in a salt environment are of fundamental interest and are potentially relevant for atmospheric chemistry, in particular sea-salt aerosols. Here, we found evidence for lactone formation upon infrared multiple photon dissociation (IRMPD) of non-covalent bromoalkanoate complexes as well as bromoalkanoate embedded in sodium iodide clusters. The mechanism of lactone formation from bromoalkanoates of different chain lengths is studied in the gas phase with and without salt environment by a combination of IRMPD and quantum chemical calculations. IRMPD spectra are recorded in the 833-3846 cmT¹ range by irradiating the clusters with tunable laser systems while they are stored in the cell of a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The measurements of the binary complex Br(CH2)_mCOOH·Br(CH2)_mCOO^- for m = 4 indicate valerolactone formation without salt environment while lactone formation is hindered for longer chain lengths. When embedded in sodium iodide clusters, butyrolactone formation from 4-bromobutyrate seems to take place already during formation of the doped clusters in the electrospray process, evidenced by the infrared (IR) signature of the lactone. In contrast, IRMPD spectra of sodium iodide clusters containing 5-bromovalerate contain signatures for both valerate as well as valerolactone. In both cases, however, a neutral fragment corresponding to the mass of valerolactone is eliminated, indicating that ring formation can be activated by IR light in the salt cluster. Quantum chemical calculations show that already complexation with one sodium ion significantly increases the barrier for lactone formation for all chain lengths. IRMPD of sodium iodide clusters doped with neutral bromoalkanoic acid molecules proceeds by elimination of HI or desorption of the intact acid molecule from the cluster.

Site-specific rate constant measurements for primary and secondary H- and D-abstraction by OH radicals: propane and n-butane

Site-specific rate constants for hydrogen (H) and deuterium (D) abstraction by hydroxyl (OH) radicals were determined experimentally by monitoring the reaction of OH with two normal and six deuterated alkanes. The studied alkanes include propane (C3H8), propane 2,2 D2 (CH3CD2CH3), propane 1,1,1-3,3,3 D6 (CD3CH2CD3), propane D8 (C3D8), n-butane (n-C4H10), butane 2,2-3,3 D4 (CH3CD2CD2CH3), butane 1,1,1-4,4,4 D6 (CD3CH2CH2CD3), and butane D10 (C4D10). Rate constant measurements were carried out over 840-1470 K and 1.2-2.1 atm using a shock tube and OH laser absorption. Previous low-temperature data were combined with the current high-temperature measurements to generate three-parameter fits which were then used to determine the site-specific rate constants. Two primary (P1,H and P1,D) and four secondary (S00,H, S00,D, S01,H, and S01,D) H- and D-abstraction rate constants, in which the subscripts refer to the number of C atoms connected to the next-nearest-neighbor C atom, are obtained. The modified Arrhenius expressions for the six site-specific abstractions by OH radicals are P1,H = 1.90 × 10(-18)T(2.00) exp(-340.87 K/T) cm(3) molecule(-1) s(-1) (210-1294 K); P1,D = 2.72 × 10(-17) T(1.60) exp(-895.57 K/T) cm(3) molecule(-1) s(-1) (295-1317 K); S00,H = 4.40 × 10(-18) T(1.93) exp(121.50 K/T) cm(3) molecule(-1) s(-1) (210-1294 K); S00,D = 1.45 × 10(-20) T(2.69) exp(282.36 K/T) cm(3) molecule(-1) s(-1) (295-1341 K); S01,H = 4.65 × 10(-17) T(1.60) exp(-236.98 K/T) cm(3) molecule(-1) s(-1) (235-1407 K); S01,D = 1.26 × 10(-18) T(2.07) exp(-77.00 K/T) cm(3) molecule(-1) s(-1) (294-1412 K).

Computational study on the reaction of atomic chlorine with 1,2-dibromoethane (CH2BrCH2Br)

In this work, the reaction mechanism and kinetics of Cl + CH2BrCH2Br → products are theoretically investigated for the first time. The optimized geometries and frequencies of all of the stationary points and selected points along the minimum-energy path for the three hydrogen abstraction channels and two bromine abstraction channels are calculated at the BH&H-LYP level with the 6-311G** basis set and the energy profiles are further calculated at the CCSD(T) level of theory. The rate constants are evaluated using the conventional transition-state theory, the canonical variational transition-state theory, and the canonical variational transition-state theory with a small-curvature tunneling correction over the temperature range 200–1000 K. The results show that reaction channel 3 is the primary channel and the calculated rate constants are in good agreement with available experimental values. The three-parameter Arrhenius expression for the total rate constants over 200–1000 K is provided.

Temperature-Dependent Kinetics Study of the Gas-Phase Reactions of OH with n- and i-Propyl Bromide

An experimental, temperature-dependent kinetics study of the gas-phase reactions of hydroxyl radical with n-propyl bromide, OH+n-C3H7Br-->products (reaction 1), and i-propyl bromide, OH+i-C3H7Br-->products (reaction 2), has been performed over wide ranges of temperatures 297-725 and 297-715 K, respectively, and at pressures between 6.67 and 26.76 kPa by a pulsed laser photolysis/pulsed laser-induced fluorescence technique. Data sets of absolute bimolecular rate coefficients obtained in this study for reactions 1 and 2 demonstrate no correlation with pressure and exhibit positive temperature dependencies that can be represented with modified three-parameter Arrhenius expressions within their corresponding experimental temperature ranges: k1(T)=(1.32x10(-17))T1.95 exp(+25/T) cm3 molecule(-1) s(-1) for reaction 1 and k2(T)=(1.56x10(-24))T4.18exp(+922/T) cm3 molecule(-1) s(-1) for reaction 2. The present results, which extend the current kinetics data base of reactions 1 and 2 to high temperatures, are compared with those from previous works. On the basis of the present data and available data from previous studies, the following bimolecular rate coefficient temperature dependencies can be recommended for the purpose of kinetic modeling: k1(T)=(1.89x10(-19))T2.54exp(+301/T) cm3 molecule-1 s-1 for reaction 1 in a temperature range 210-725 K, and k2(T)=(2.83x10(-21))T3.1exp(+521/T) cm3 molecule(-1) s(-1) and k2(T)=(4.54x10(-24))T4.03exp(+860/T) cm3 molecule(-1) s(-1) for reaction 2 in temperature ranges 210-480 and 297-715 K, respectively.

One-color two-photon mass-analyzed threshold ionization spectroscopy of ethyl bromide through a dissociative intermediate state

Mass-analyzed threshold ionization (MATI) spectra of ethyl bromide were obtained using one-color two-photon ionization through a dissociative intermediate state. Accurate values for the adiabatic ionization energy have been obtained, 83099+/-5 and 85454+/-5 cm(-1) for the X1 2E and X2 2E states of the ethyl bromide cation, respectively, giving a splitting of 2355+/-10 cm(-1). Compared with conventional photoelectron data, the two-photon MATI spectrum exhibited a more extensive vibrational structure with a higher resolution, mainly containing the modes involving the dissociation coordinate. The observed modes were analyzed and discussed in terms of wave packet evolving on the potential-energy surface of the dissociative state.