Study On The Photoexcitation And Photodissociation Dynamics Of CO₂⁺

This paper presents the experimental studies on the photofragment excitation (PHOFEX) spectrum (the depletion spectrum of parent CO2+and the enhanced spectrum of photofragments CO+, O+and C+) and photodissociation dynamics of the small molecular ions including oxygen CO2+. The main results are summarized as following:The [1+1] two-photon dissociation spectra of CO2+via A2Πu1/2 (υ1υ20)←X2Πg1/2(000) transitionsIn the wavelength range of 235-354 nm we have obtained the mass-resolved [1+1] two-photon dissociation spectra of CO2+via A2Πu,1/2(υ1υ20)←X2Πg,1/2(000) transitions by preparing CO2+ ions in the X2Πg,1/2(000) state via [3+1] multiphoton ionization of CO2 molecules at 333.06 nm. The vibronic bands of (υ120;υ1=0-11)μ2Π1/2 and (υ120;υ1=0-6)κ2Π1/2 involving the bending mode of CO2+(A2Πu,1/2) were assigned. The spectroscopic constants of Te=27908.9±1.1 cm-1 (above CO2+(X2Πg,1/2)), v1=1126.00±0.36 cm-1,χ11=-1.602±0.005 cm-1, v2(μ2Π1/2)=402.5±13.3 cm-1, and v2(K2Π1/2)=493.1±23.6 cm-1 for CO2+(A2Πu,1/2) are deduced from the data of the A2Πu,1/2(υ1υ20)←X2Πg,1/2(000) transitions. The observed intensity reversal between (500)2Π1/2 and (420)μΠ1/2 can be attributed to the conformational variation of CO2+(A2Πu,1/2) from linear to bent, then the conversion potential barrier is estimated to be 5209 cm-1 above CO2+(A2Πu,1/2 (000)). The wavelength and level dependence of the photofragment branching ratios have been measured and the dissociation dynamics of CO2+ via A2Πu,1/2 state is discussed.The [1+1] two-photon dissociation spectra of CO2+(X2Πg(Ω=3/2)) via A2Πu,3/2 (υ1υ20)←X2Πg,3/2(000) The mass-resolved [1+1] two-photon dissociation spectra of CO2+(X2Πg (Ω=3/2)) via A2Πu,3/2(υ1υ20)←X2Πg,3/2(000) transitions were studied by introducing a dissociation laser with a wavelength of 283-353 nm. CO2+ (X2Πg,3/2(000)) was prepared by the [3+1] multi-photon ionization of CO2 at 333.69 nm. The vibronic bands of (υ120;υ1=0-5)μ2Π3/2 and (υ120;υ1=0-5)κ2Π3/2 involving the bending mode of CO2+(A2Πu,3/2) were assigned. Based on the assignments, the spectral constants of Te=27969.3±1.2cm-1 [above CO2+(X2Πg,3/2)], v1=1125.89±0.53 cm-1,χ11=-0.659±0.010 cm-1, v2(μ2Π3/2)=429.5±9.7 cm-1, and v2(k2Π±3/2)=528.7±8.0 cm-1 for CO2+(A2Πu,3/2) were deduced. The photodissociation dynamics of CO2+via A2Πu,3/2(υ1υ20)←X2Πg,3/2(000) transitions are discussed.Study on the [1+1'] photodissociation spectra of CO2+via C2∑g+←B2∑u+(000) /A2Πu1/2 (000/100)←X2Πg,1/2(000) transitionsBy preparing CO2+ ions in the X2Πg,1/2(000) state via [3+1] multiphoton ionization of CO2 molecules at 333.06nm, we have obtained the mass-resolved [1+1'] two-photon dissociation spectra of CO2+ via the C2∑g+(υ1,υ2,0)←C2∑u+(000) /A2Πu(000; 100)←X2Πg,1/2(000) transitions by fixing the first dissociation laser at 289.77nm,351.24nm,337.90nm to excite the CO2+to B2∑u+(000),A2Πu(000), A2Πu(100) state, separately, and scanning the second dissociation laser in the wavelength range of 557-759nm. The original CO2+(C2∑g+(000)) position of 45120±3cm-1 above CO2+(X2Πg,1/2(000)) and the spectroscopic constants of v1= 1400±5 cm-1, v2=620±8cm-1 and v3=2909cm"'for CO2+(C2∑g+) are deduced from the C2∑g+(υ1,υ2,0)←B2∑u+(000)/A2Πu(000; 100)←X2Πg,1/2(000) transition data. The dependence of the product branching ratios [CO+]/[O+] of CO2+(C2∑g+) on the vibration levels have been observed and the dissociation dynamics of CO2 via C2∑g+ state is discussed.