Mechanism of formation of the MV<sup>.+</sup> radical during the UV excitation of methylviologen
Submitted by Carlos E Crespo-Hernández on
PDF version| Title | Mechanism of formation of the MV.+ radical during the UV excitation of methylviologen |
| Publication Type | Journal Article |
| Year of Publication | 2001 |
| Authors | Mendez, EE, Crespo-Hernández, CE, Figueroa, R, Arce, R, Quinones, E |
| Journal | J. Photochem. Photobiol. AJ. Photochem. Photobiol. AJ. Photochem. Photobiol. A |
| Volume | 142 |
| Pagination | 19-24 |
| Abstract | The UV illumination of diluted aqueous solutions of methylviologen (MV2+) leads to the formation of the methylviologen radical (MV.+), without the use of microheterogeneous materials or sacrificial electron donors. In the absence Of O-2 the MV.+ radical remains in solution for hours. The formation mechanism of MV.+ was investigated employing the laser flash photolysis technique. The hydrated electron (e(aq)(-)) band and the characteristic bands of the MV.+ radical at 395 and 605 nm were detected in the MV2+ transient absorption spectra. This indicates that (1) MV2+ is ionized at 266 nm and (2) the e(aq) (-) + MV2+ reaction is a source of the MV.+ radical. The rate constant for this reaction was measured at pH 6.5 to be (3.8 +/- 0.1) x 10(10) M-1 s(-1) and its magnitude is in good agreement with literature values. The ionization quantum yield of 0.16 was determined for MV2+ using KI as a reference actinometer. The photodestruction quantum yield of MV2+ was calculated to be (8.7 +/- 0.5) x 10(- 3) molecules/quantum. The formation quantum yield of MV.+ was measured at the two absorption maxima of the radical, phi (395 nm) = (4.8 +/- 0.5) x 10(-3) and phi (605 nm) = (5.1 +/- 0.3) x 10(-3) molecules/quantum. (C) 2001 Elsevier Science B.V. All rights reserved. |
| Short Title | J. Photochem. Photobiol. A-Chem. |
| Alternate Journal | J. Photochem. Photobiol. A-Chem. |
