## 2 Experiments
### Gaseous Products Study  
For the determination of the gaseous products of reaction (R1), the two simulation chambers were used depending on the employed detection technique: FTIR spectroscopy, CG-MS, or PTR-ToF-MS.  
When products were detected by FTIR spectroscopy, the 16-L cell and the same instrumentation used in the kinetic experiments described above were used again [19; 20]. Experiments were run by irradiating the air mixture with T2M2B ((2.3-5.3) \(\times\) 10\({}^{14}\) molecule cm\({}^{-3}\)) and Cl\({}_{2}\) ((6.0-7.7) \(\times\) 10\({}^{14}\) molecule cm\({}^{-3}\)) in the cell.  
A GC-MS system (Thermo Electron, models Trace GC Ultra and DSQ II, Milan, Italy) and a PTR-ToF-MS (IONICON, model PTR-TOF 4000, Innsbruck, Austria) were coupled to the 264-L chamber, but in independent experiments. The GC-MS was equipped with a BPX35 column (\(30\) m \(\times\) 0.25 mm ID \(\times\) 0.25 \(\upmu\)m, SGE Analytical Science, Milton Keynes, UK) [19] working at a temperature ramp that ranged between 40 and 250 \({}^{\circ}\)C. The Solid-Phase Microextraction (SPME) was used as sampling technique with a 50/30 \(\upmu\)m divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber (Supelco) that was exposed to the gas mixture in the chamber during 5 min. In this case, the initial concentrations of T2M2B and Cl\({}_{2}\) ranged between 5.4 and 8.6 \(\times\) 10\({}^{14}\) molecule cm\({}^{-3}\) and between 5.1 and 8.4 \(\times\) 10\({}^{14}\) molecule cm\({}^{-3}\), respectively.  
The PTR-ToF-MS employs H\({}_{3}\)O\({}^{+}\) as the primary ion in the proton transfer procedure. The mass spectra of the reactive gas mixture were recorded with a time resolution of 20 s and the detected mass range was set between 29 and 390.86 amu. The E/N factor of the instrument was set at 137 Td and products were quantified by using the transmission calibration of the instrument. Since this instrument is more sensitive than the FTIR spectrometer and the SPME/GC-MS system, to avoid saturation of the intensity, the initial concentration of T2M2B and Cl\({}_{2}\) in the chamber was reduced with respect to that employed in the FTIR and GC-MS experiments: (1.9-2.1) \(\times\) 10\({}^{13}\) molecule cm\({}^{-3}\) for T2M2B and (2.3-2.4) \(\times\) 10\({}^{13}\) molecule cm\({}^{-3}\) for Cl\({}_{2}\). In addition, to get intensity signals below the saturation limit, the gas sample had to be diluted with an air flow at the inlet of the PTR-ToF-MS by means of a dynamic inlet dilution system. A dilution factor of 1/5 was enough to not saturate the intensity signal. This dilution factor was achieved taking into account that the fixed flow going into the reaction chamber of the PTR-ToF-MS is 80 sccm (standard cubic centimeter per minute), and setting the additional inlet flow at 70 sccm, so the total flow going through the inlet was 150 sccm. Since the dilution flow was set at 120 sccm, only 30 sccm of the total 150 sccm going through the inlet were sampled from the 264-L chamber.  
In all the experiments, the products of the reaction of T2M2B with Cl were monitored during 60 min, and tests were done to establish the products generated during the UV light exposure of T2M2B and by its reaction with Cl\({}_{2}\) in the dark. The product yield of a product (Y\({}_{\text{Prod}}\)) was determined as the ratio of its concentration, [Prod], and the loss of reactant, \(\Delta\)[T2M2B]:  
\[\text{Y}_{\text{Prod}}=\frac{[\text{Prod}]}{\Delta[\text{T2M2B}]}. \tag{2}\]