## 1 Introduction  
Ofloxacin (Scheme 1) belongs to the class of fluoroquinoline antibiotics. These broad-spectrum bactericides share a bicyclic core structure related to the substance 4-quinolone [1, 2]. There is an F atom on the 4-quinolone unit; a methyl-substituted piperazine ring, a carboxyl group, and a methyl-substituted oxazine ring are also attached to the double-ring structure. Due to the methyl group on the oxazine ring, this molecule is chiral with enantiomers named levofloxacin and dextrofloxacin. Ofloxacin contains both enantiomers. The antibacterial effect of levofloxacin is higher than those of ofloxacin and dextrofloxacin [3]. The carboxyl group dissociates with a pKa value of 5.45; at neutral pH, the molecule is an anion [4]. Due to the frequent use of ofloxacin and levofloxacin in medical practice, they are regularly found in surface waters (100-300 mg dm\({}^{-3}\), [5, 6]). These medicines and many other pharmaceuticals enter surface waters predominantly through the purified wastewaters released by wastewater treatment plants, because the traditional purification techniques (biological treatment) are not effective enough in their removal. For the elimination of different pharmaceuticals from purified wastewater, new techniques, the so-called advanced oxidation processes (AOP), are recommended. In these processes, short-lived reactive radicals (hydroxyl radicals (\({}^{\bullet}\)OH), sulfate radical anions (SO\({}_{\bullet}\)\({}^{\bullet-}\))) induce the solute degradation (recent examples: [7,8]). \({}^{\bullet}\)OH is the main reactant in most AOP, and the different techniques differ mainly in the way of \({}^{\bullet}\)OH generation: in the Fenton, photo-Fenton, and electro-Fenton processes, the decomposition of hydrogen peroxide; in the sonochemical techniques, cavitation; in photocatalytic processes, photon-catalyst interactions; and in high-energy ionization radiation treatment, water degradation (see later) produces \({}^{\bullet}\)OH. Here we use the latter technique. A good description of the different techniques was published in the book _Advanced Oxidation Processes for Water Treatment_, edited by [PERSON] [9]. The literature has reported on very few radiolytic studies with fluoroquinolones [3,10, 11, 12, 13]. In the published works, mainly the elementary steps of \({}^{\bullet}\)OH reactions were investigated by using pulse radiolysis with transient kinetic techniques [10,14, 15, 16]. The rate constant of \({}^{\bullet}\)OH reactions with fluoroquinolones was found to be in the diffusion limited range, \(k_{\bullet\text{OH}}=6.2\)-\(8.1\times 10^{9}\) mol\({}^{-1}\) dm\({}^{3}\) s\({}^{-1}\). A similar value, \(7.65\times 10^{9}\) mol\({}^{-1}\) dm\({}^{3}\) s\({}^{-1}\), was measured for a model compound of fluoroquinolones (6-fluoro-4-oxo-1-4-dihydro-3-quinoline carboxylic acid), which does not contain the piperazine and oxazine rings [14]. The comparable rate constant suggests that the core aromatic ring structure is the main target of \({}^{\bullet}\)OH. In agreement with this suggestion, products revealing hydroxylation of the quinolone core form with high abundance [10, 11, 12]. Defluorination is also an important degradation pathway. \({}^{\bullet}\)OH addition to the carbon-fluorine position and rapid HF elimination may be the possible reaction path. By irradiating aerated 0.1 mmol dm\({}^{-3}\) concentration solutions with a 1 KGy dose, \(-95\%\) of the fluoroquinoline molecules undergo chemical transformation, the majority of the original molecules disappear, and derivatives (products) appear. Using 2 KGy, most of the products formed first also undergo some form of transformation [3, 12, 14, 15, 16, 17]. During irradiation in unbuffered solution, the pH decreases from 6-7 to \(-4\)[3,17]. As mentioned before, the basic chemical reactions between \({}^{\bullet}\)OH and several fluoroquinolone antibiotics were investigated in the past.