New Development in Chemistry of Hypervalent Radicals Approach from the Gas-phase

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In order to reveal the role of hypervalent radicals in chemical reactions including those in biological chemistry, we have studied on the following three subjects.1. The electronic structures of Na-2^-(H_2O)_n (n〓6), which have a similar loosely-bounded electron to NH_4 have been investigated by a photoelectron spectroscopy (PES) to examine the solvation of sodium aggregates in small water clusters, From the analysis of the PES bands for the transitions from the anion to the neutral ground and first excited states derived from Na_2 (1^1Σ_g^+) and Na_2(1^3Σ_u^+) it is found that the Na_2-Na^+(H_2O)_n^-type electronic state grows with increasing cluster size, which can be regarded as a sign of the solvation of Na_2 with ionization of the hydrated Na.2. Ionization potentials (IPs) of NR_4(CH_3OH)_m (NH_3)_n radicals produced by an ArF excimer laser photolysis of ammonia-methanol mixed clusters are determined by the photoionization threshold measurements. The observed IPs show the different evolutions with increasing the number of ammonia and methanol solvents. We have also examined the formation and relaxation dynamics of NH_4(CH_3OH)_m(NH_3)_n clusters produced by photolysis of ammonia-methanol mixed neutral clusters using a time-resolved pump-probe method with femtosecond pulse lasers. From the detailed analysis of the time evolutions of the protonated cluster ion, NH_4(CH_3OH)_m(NH_3)_n, the kinetic model is constructed.3. A photodissociation spectrometer, containing a spray ionization source and a temperature-variable multipoleion trap, has been constructed to examine the structure and reactivity of gas phase biological molecular ionsat various temperatures. Ultraviolet (UV) and infrared (IR) photodissociation spectra of protonatedalanyltryptophan (Ala-TrpH+) and tryptophanylglycine (Trp-GlyH+) have been investigated to examine the effect of proton on the electronic structure and reactivity of the dipeptides.