Quanta ray mopo sl

The matrix-isolated samples were irradiated at the frequency of the second OH stretching overtones using two monochromatic near-IR light sources: (i) tunable near-IR light (full range) generated as the idler beam of a Spectra Physics Quanta-Ray MOPO-SL optical parametric oscillator (fwhm 0.2 cm À1 , pulse energy 10 mJ), pumped with a pulsed Nd:YAG laser (10 ns, repetition rate 10 Hz), and (ii) tunable near-IR light (B10 500-10 100 cm À1 ) generated by a continuous wave diode laser Toptica DLC TA PRO (fwhm o1 MHz, up to 3 W). In a typical experiment, irradiation was carried out for 20 min using 120 mW of power. Similar results were obtained using both near-IR light sources.

Commercial AB (Fluka, purity 98%), DAB (Sigma-Aldrich, purity 97%), and AT (Sigma-Aldrich, 98%) were placed in a glass tube connected to the vacuum chamber of the cryostat through a shutoff valve. The compound vapors were deposited with a large excess of the matrix gas (argon N60 or xenon N48, Air Liquide) onto a CsI substrate cooled using a closed-cycle helium refrigerator (APD Cryogenics DE-202A). The deposition temperature was 15 and 30 K for argon and xenon matrices, respectively. The infrared spectra were recorded in the 4000-400 cm À1 range with 0.5 cm À1 resolution using a Nicolet 6700 FTIR spectrometer equipped with DTGS and MCT-B detectors and a Ge/KBr beam splitter. The matrices were irradiated through a quartz window of the cryostat using tunable narrowband (0.2 cm À1 spectral width) light provided by a Spectra Physics Quanta-Ray MOPO-SL optical parametric oscillator (OPO) pumped with a pulsed Nd:YAG laser (repetition rate = 10 Hz, duration B10 ns). In the visible range (440-600 nm), the signal beam of the OPO was used (pulse energy of B30-40 mJ). In the UV range (230-440 nm), the frequency-doubled signal or idler beam was used (pulse energy of B3 mJ). The selection of the irradiation wavelengths was guided by the absorption spectra of the compounds in solution (Fig. S2,ESI †).