Chemical Physics Letters 618 (2015) 219–224 Contents lists available at ScienceDirect Chemical Physics Letters jou rn al hom epage: www.elsevier.com/locate/cplett UV-tunable laser induced photolysis of matrix isolated anisole Justyna Krupa, Maria Wierzejewska ∗ Faculty of Chemistry, University of Wroclaw, Joliot-Curie 14, 50-383 Wroclaw, Poland a r t i c l e i n f o Article history: Received 9 October 2014 In final form 11 November 2014 Available online 15 November 2014 a b s t r a c t Photochemical transformations of matrix-isolated anisole (AN) were induced using UV-tunable laser radiation. The progress of reactions was followed by FTIR spectroscopy that allowed for identification of several photoproducts. They were distinguished according to their different patterns of bands intensity changes during the progress of photolysis. Among these products the phenoxy and methyl radicals were observed that recombined to form two isomers of methylcyclohexadienone (ANO). The ortho isomer readily decomposed producing different isomers of long-chain ketene and bicyclohexenone molecules. Decarbonylation was also detected in the studied systems. Interpretation of the experimental observa- tions was supported by DFT calculations at the B3LYP/6-311++G(2d,2p) level. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Anisole (methoxybenzene) is an interesting molecule because of several reasons. Although it is mainly made synthetically many of its derivatives such as anethole, estragole or p-anisaldehyde may be found both in natural and artificial fragrances [1]. It is often used as a precursor for other synthetic compounds. Most of the aromatic rings present in lignin that is a major component of plant material contain methoxy groups. Thus, anisole serves as an important model compound and understanding its decomposition pathways is closely related to the biomass combustion. Because of these reasons the pyrolysis of anisole and related compounds has recently attracted attention and was found to produce a num- ber of interesting radicals [2,3–10]. It was shown for anisole [2,3] using a hyperthermal tubular reactor and time-of-flight mass spec- trometer that the first step in the thermal decomposition of this compound was the C O bond breakage and formation of the methyl and phenoxy radicals, followed by carbon monoxide liberation to form cyclopentadienyl radical. The latter radical is an important species in combustion processes due to its role in the formation of polycyclic aromatic hydrocarbons [2]. At higher temperature the cyclopentadienyl radical decomposes to propargyl radical and acetylene [5]. Although the thermal decomposition of anisole has been stud- ied in detail much less is known on UV photolysis of this compound. Here we report the UV-tunable laser induced decomposition reac- tions of the anisole isolated in a low-temperature argon matrix. ∗ Corresponding author. E-mail address: maria.wierzejewska@chem.uni.wroc.pl (M. Wierzejewska). 2. Experimental 2.1. Martix isolation studies and UV irradiation experiments Anisole obtained from Aldrich was degassed and used with- out further purification. Anisole/Ar mixtures were prepared in a vacuum line by standard procedure. Low temperature (11 K) was obtained by means of a closed cycle helium refrigerator (APD- Cryogenics ARS-2HW) and measured directly at the sample holder by a silicon diode sensor working with a digital controller (Scien- tific Instruments, model 9700). Infrared spectra were measured in a transmission mode with 0.5 cm -1 resolution using a Bruker IFS 66 Fourier Transform spectrometer equipped with a liquid N 2 cooled MCT detector. After the infrared spectra of the deposited matrices were recorded, the samples were irradiated with tunable UV light pro- vided by the frequency doubled signal beam of a pulsed (7 ns, with a repetition rate of 10 Hz and average pulse energy of 3.9 mJ) opti- cal parametric oscillator (OPO) Vibrant (Opotek, Inc.) pumped with a Nd:YAG laser (Quantel). The UV wavelength was automatically measured by the wavemeter integrated into the system with addi- tional access to the Closed-Loop Tuning function allowing for better than 1 nm resolution. 2.2. Computational details All calculations for the precursor molecule and putative photo- products were performed with the Gaussian program package [11]. Structures were optimized at the B3LYP/6-311++G(2d,2p) level. The associated force constant matrices were calculated at the same level of theory to evaluate harmonic and anharmonic frequencies and http://dx.doi.org/10.1016/j.cplett.2014.11.020 0009-2614/© 2014 Elsevier B.V. All rights reserved.