Dynamics and mechanism of the non-adiabatic transitions from the ungerade I2(D0+u) state induced by collisions with rare gas atoms

Abstract

The stepwise three-photon two-color laser excitation scheme is used for selective population of the first-tier ion-pair D0(+)(u) state of molecular iodine. Collection and analysis of the luminescence after the excitation of the v(D) = 6, 8, 13 and 18 vibronic levels of the D state in the pure iodine vapor and the gas-phase mixtures with He, Ar and Xe provide the total and, whenever possible, partial rate constants for the collision-induced non-adiabatic transitions to the other ion-pair states of the first tier. Comparison with the analogous data obtained previously for the non-adiabatic transitions from the E0(+)(g) state reveals the similarity between two cases. For He, the D ↔ E transitions are preferable, whereas for Ar and Xe transitions to the D' and β states dominate at v(D) = 6, 8 and 13, in accord with the statistical considerations. Efficient population of the δ state at v(D) = 18 in Ar and Xe is the most prominent non-statistical feature observed. The vibrational product state distributions for the D → E transitions are also obtained. In contrast to the previously studied E → D transition, they show significant positive vibronic energy transfer. The measurements for He and Ar are accompanied by the quantum scattering calculations that reproduce well the main qualitative features of the experimental results.

Non-adiabatic transitions from I2(${E} {\rm 0}_{g}^{+} $Eg+ and ${D}0_{u}^{+} $Du+) states induced by collisions with M = I2(${X}0_{g}^ + $Xg+) and H2O

“…Cross section of the complex formation is σ c ≈ 80 Å 2 . 23 The CINAT rate constants depending on long-range, transition I 2 (E-D) dipole-permanent I 2 (X) quadrupole, −C 4 /R 4 , interaction 21,38 decreases strongly in this case due to large energy mismatch. (Table III) (Table III).…”

“…[16][17][18][19] as well as water impurity 20 − −−− → D) CINAT rate constants. Very recently, the first experimental results for the ungerade D-state CINATs in collisions of molecular iodine with the rare gases Rg = He, Ar, Xe, as well as some preliminary data for the collisions with the I 2 (X) molecule 21 were reported.…”

Dipole moment functions of the iodine D′2g–A′2u, {\rm D}0_u^ + \hbox{--} {\rm a}^{\prime}\mathop 0\nolimits_g^ +, D0+u–X0g+and {\rm E}0_g^ + \hbox{--}\mathop {{\rm B}0}\nolimits_u^ + transitions

“…A detailed description of experimental apparatus for measurements of the excitation and luminescence spectra has been given elsewhere (see [18][19][20][21][22] and references therein). We utilized the Quantel system consisting of YG981C Nd:YAG and two tunable dye TDL90 lasers.…”

“…(see [21] and references therein), and the three-step, threephoton, two-and three-colour hν 1 + hν f +hν 1 (hν 1 + hν f + hν 2 ) excitation schemes…”

“…We use emission spectroscopy for studying collisioninduced nonadiabatic transitions (CINATs) between iodine IP states (see [18][19][20][21] and references therein). We have studied CINATs from the E and D states of the first tier and observed that all other five states (γ , β, δ2 u , D 2 g and D or E) of the tier are populated.…”