Structure of free radicals

Vibrationally resolved spectra of HCl"2"+ appear to show five vibrational levels for the X"3#SIGMA#"- state, whereas calculations of vibrational levels supported by ab-initio potential energy curves have been able to locate only three vibrational levels; this discrepancy is resolved by considering vibrational states in the continuum above the barrier maximum. A low resolution spectrum produced from first principles is compared with a threshold photoelectrons in coincidence (TPEsCO) spectrum, and shows that care must be taken in the inversion of vibrational spectroscopic data for molecular dications. A spectrum of the X"3#SIGMA#"- state of DCl"2"+ was simulated that successfully predicted the structure subsequently observed with TPEsCO measurements. A search was conducted for transitions in the 7<-6 and 8<-7 vibrational bands of the A"2#PI# state of NO"2"+ with a fast-ion beam/laser beam spectrometer (FIBLBS). No spectra were observed. Calculations made utilising the most recent ab-initio potential energy surface describing the A"2#PI# electronic state predicted that an improvement by a factor of between 2 and 20 in the signal to noise ratio obtained would be sufficient to render the transitions observable with the FIBLBS. The FIBLBS was also used to search for infrared transitions within the v=2<-1 band of the X"3#SIGMA#"- state of H"3"7Cl"2"+. Pointwise frequency scanning was used to scan over the very broad (#approx#10cm"-"1) resonances predicted. The measured spectrum yields encouraging structure which warrants further investigation. The FIBLBS was modified to observe a microwave spectrum of a forbidden pure rotation transition in the 1s#sigma#_g state of H_2"+. The 19,1<-19,0 transition was observed in single and double resonance with a frequency of (14961.7#+-#1.1) MHz. Infrared diode laser transient absorption spectroscopy was used to study the chemical kinetics of the reaction of ethyl radicals with oxygen. A bimolecular rate constant of (1.77#+-#0.07)*10"-"1"2cm"3. molecule"-"1.s"-"1 was measured for the reaction at 333K. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:DXN039940 / BLDSC - British Library Document Supply CentreGBUnited Kingdo