Ultraviolet Photofragmentation Spectroscopy of Alkaline Earth Dication Complexes with Pyridine and 4-Picoline (4-Methyl pyridine)

作者：Stewart Hamish; Wu Guohua; Ma Lifu; Barclay Michael; Vieira Andreia Dias; King Andrew; Cox Hazel^*; Stace Anthony J

来源：Journal of Physical Chemistry A, 2011, 115(25): 6948-6960.

DOI：10.1021/jp112171j

A detailed experimental and theoretical study has been undertaken of the UV photofragmentation spectroscopy of the alkaline earth metal dications Mg2+, Ca2+, and Sr2+ complexed with pyridine and 4-methyl pyridine (4-picoline). The ion complexes have been prepared using the pick-up technique and held in an ion trap where their internal temperature has been reduced to < 150 K. Exposure of the trapped ions to tunable UV laser radiation leads to the appearance of photofragments with intensities that show significant variation as a function of wavelength. For all three metal dications, the resultant spectra show evidence of resolved features. Time-dependent density functional theory (TDDFT) has been used to identify possible electronic transitions that might be present in the [M(pyridine)(4)](2+) complexes (M = Mg, Ca, and Sr) within the wavelength range studied. These calculations show that the spectra are dominated by strong pi* <- pi and weaker pi* <- n transitions localized on the pyridine ligands. The calculations correctly identify those regions of the experimental spectra where UV transitions begin to occur in the complexes and also the wavelengths at which absorption maxima are reached; however, more subtle features of the spectra are difficult to assign with confidence.

• 出版日期2011-6-30