Power-scalable Ho:YAG slab laser intracavity side-pumped by a Tm:YLF slab laser

We report the first demonstration of an intracavity side-pumped Ho:YAG slab laser, delivering 13W at 2.09µm and discuss the advantages of this scheme as an approach for power scaling

Oxidation of aqueous sulfur dioxide by peroxymonosulfate

Recent model calculations suggest that peroxymonosulfate may constitute a significant fraction of the total sulfur budget in remote tropospheric water droplets such as cloud, fog, and rain. However, little is known about the oxidation of dissolved SO_2 by peroxymonosulfate (HSO_5^-). We have found in aqueous solution that the rate of S(IV) oxidation is comparable to the rate of oxidation of S(IV) by hydrogen peroxide and that HSO_4^- is the only detectable oxidation product. We propose a mechanism in which the rate-determining step involves the acid-catalyzed decomposition of a peroxide-bisulfite intermediate to disulfate ion, S2_7O^(2-), and ultimately to sulfuric acid. The rate equation for this mechanism is -d[HSO_3^-]/dr = k_1(k_2/k_(-1))K_(a1){H^+}[HSO_5^-][S(IV+)]/(1 + (k_2/k_(-1){H^+})(k_(al) + {H+))), where k_1 = 1.21 x 10^6 M^(-1) s^(-1), k_2/k_(-1) = 5.9 M^(-1), k_1k_2/k^(-1) = 7.14 x 10^6 M^(-2) s^(-1), K_(a1) = 2.64 x 10^(-2) M at 5 ºC, and µ = 0.2 M. The activation parameters are ΔH_(k1) = 25.74 ± 0.77 kJ mol^(-1) and ΔS_(k1)^*= -88.1 ± 2.7 J mol^(-1) K^(-1)

Kinetics, mechanism and thermodynamics of the reversible reaction of methylglyoxal (CH_3COCHO) with sulfur (IV)

At pH ≤ 2 the following rate law for the formation of hydroxyacetylmethaneulfonate (HAMS) from methylglyoxal (MG) and S(IV) (H_2O•SO_2, SO_3^(2-))is obtained: d[HAMS]/dt = ((k_0α_1[H^+]/K_(a0)) + k_1α_1 + k_2α_2)[S(IV)][MG]_0)/(1 + K_d + K_d[H^+]/K_(a0)), where α_1 and α_2 are the fractional concentrations of HSO_3^- and SO_3^(2-), respectively; k_0, is the rate constant for the reaction of HSO_3^- with the carbocation aldehyde species (CH_3COC^+HOH); k_1, and k_2 are the rate constants for the reaction of unhydrated MG with HSO_3^- and SO_3^(2-), respectively; K_d is the dehydration constant of hydrated MG; and K_(a0) is the acid dissociation constant of the carbocation. At pH ≥4 the rate of formation of HAMS is determined by the rate of dehydration of the diol form of (hydrated) MG: d[HAMS]/dt = k_d[MG]/(l + K_d + _Kd [H^+]/K_(a0)), where k_d = k_w + k_H[H^+] + kOH[OH^-] + k_A[A] + kB_[B], and k_w is the intrinsic (water) rate constant; k_H and k_OH) are the specific acid and base rate constants; and k_A and k_B are the general acid (A) and base (B) rate constants. Between pH 2 and 4, biexponential kinetics are observed because, under our conditions, the rates of dehydration and of S(IV) addition become comparable. Over the pH range 0.7-7.0, the dissociation of HAMS follows the rate law: d[S(IV)]/dt = ((k_(-0)[H^+] + k_)-1) + k_(-2)K_(a3)/[H^+])K_(a4)[H^+][HAMS])/[H^+]]^2 + K_(a4)[H^+] + K_(a3)K_(a4)) where k_(-0) k_(-1), and k_(-2) are the reverse of the analogous forward rate constants defined above and K_(a3) and K_(a4) are the acid dissociation constants of the sulfortate anion and the sulfonic acid, respectively. Experiments to determine the effect of temperature on the rate (and equilibrium) constants indicate a marked effect of ΔS^* (and ΔS_(298)) on the relative magnitude of these constants

Kinetics and mechanism of the oxidation of aqueous hydrogen sulfide by peroxymonosulfate

The stoichiometry and mechanism of the oxidation of aqueous S(-II) by HSO_5^-, is similar to the oxidation of S(-II) by H_2O_2, but the rate of oxidation by HSO_5^-; is 3-4 orders of magnitude faster than the corresponding reaction with H_2O_2. A two-term rate law of the following form is found to be valid for the pH range of 2.0-6.3: -d[S(-II)]/dt = k_1[H_2S][HSO_5^-] + k_2K_(a1)[H_2S][HSO_5^-]/[H^+], where k_1 = 1.98 X 10^1 M^(-1) s^(-1),k2 = 1.22 X 10^4 M^(-1) s^(-1), and K_(al) = [H^+][HS^-]/[H_2S] = 2.84 X 10^(-8) M at 4.9 °C, µ = 0.2 M, and [S(-II)] = [H_2S] + [HS^-] + [S^(2-). At high pH and high [HSO_5^-]/[S(-II)] ratios SO_4^(2-) and H^+ formation are favored, whereas at low pH and low [HSO_5^-]/[S(-II)] ratios elemental sulfur (S_8) is favored as the principal reaction product. Peroxymonosulfate is a monosubstituted derivative of hydrogen peroxide that is thermodynamically more powerful as an oxidant than H_2O_2 and kinetically more reactive. These properties make HSO_5^- a potentially important oxidant in natural systems such as remote tropospheric clouds and also a viable alternative to H_2O_2 for the control of malodorous sulfur compounds and for the control of sulfide-induced corrosion in concrete sewers

Aldehyde-bisulfite adducts: prediction of some of their thermodynamic and kinetic properties

Stability constants (K_1) for the reaction of acetaldehyde and hydroxyacetaldehyde with NaHSO_3, determined spectrophotometrically in aqueous solution, were found to be (6.90 ± 0.54) x 10^5 M^(-1) and (2.0 ± 0.5) x 10^6 M^(-1) respectively, where K_1 (corrected for aldehyde hydration) = [RCH(OH)SO_3^-]/[RCHO][HSO_3^-] (µ = 1 0.2 M; 25 °C). Acid dissociation constants (pK_(a3)) of a series of α-hydroxyalkanesulfonate salts, RCH(OH)SO_3^-, were found to be 11.46 (CH_3-), 11.28 (H-)10.30(HOCH_2-),10.33 (C_(6-)H_5-),10.31 (CH_3CO-), and 7.21 (Cl_3C-)(µ = 0 M; 25 °C). Simple straight-line relationships were found to exist between Taft's σ^* parameter and a number of thermodynamic and kinetic properties of some aldehydes. K_1, K_(a3), and the rate constant for nucleophilic addition of SO_3^(2-) all increase linearly with σ^*. Carbonyl species such as halogenated derivatives of acetaldehyde, certain β- and γ-dicarbonyl aldehydes, and perhaps also some highly (halogen) substituted ketones, ie., all those species with ∑σ* ≥ ~1.5 (aldehydes) or ∑σ* ≥ ~2.5 (ketones), could be important S(IV) reservoirs