title: Ultraviolet photofragmentation spectroscopy of alkaline earth dication complexes with pyridine and 4-picoline (4-methyl pyridine).
abstract: A detailed experimental and theoretical study has been undertaken of the UV photofragmentation spectroscopy of the alkaline earth metal dications Mg(2+), Ca(2+), and Sr(2+) 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 π* ← π and weaker π* ← 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.
authors.affiliation: Department of Physical and Theoretical Chemistry, School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kindom.
authors.forename: Hamish
authors.initials: H
authors.lastname: Stewart
authors.forename: Guohua
authors.initials: G
authors.lastname: Wu
authors.forename: Lifu
authors.initials: L
authors.lastname: Ma
authors.forename: Michael
authors.initials: M
authors.lastname: Barclay
authors.forename: Andreia Dias
authors.initials: AD
authors.lastname: Vieira
authors.forename: Andrew
authors.initials: A
authors.lastname: King
authors.forename: Hazel
authors.initials: H
authors.lastname: Cox
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Stace