Collision-partner dependence of energy transfer between the CH a 2Δ and B2- states

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We have investigated experimentally the collision-induced electronic energy transfer between the CH A2? and B2? - states with the series of partners He, Ar, H2, N 2, CO, and CO2. Single rovibronic states of either of the near-degenerate levels A2?, v = 1, or B2? -, v = 0, were prepared by laser excitation. Collisional transfer processes were monitored by detecting dispersed, time-resolved fluorescence from the initial and product states. The microscopic rate constants for vibronically resolved transfer between the A2? and B 2?- states, vibrational relaxation within the A state, and total removal to unobserved final products were determined for each partner. In line with previous work, we find that only CO and H2 are efficient at total removal of CH A2? and B 2?-, most probably through chemical reaction. CO 2 is notably effective at A2? state vibrational relaxation, possibly through resonant vibrational energy transfer. All the partners cause transfer between CH A2? and B 2?-. An important new observation is that their efficiencies are well correlated with the strength of long-range attractive forces, as revealed through a positive correlation of the Parmenter-Seaver type. The vibronic branching to A2?, v = 0 and 1 from B 2?-, v = 0 is found to be significantly collision-partner-dependent and not well predicted by energy gap scaling laws. We do not find any enhanced effectiveness in B2?- to A2? coupling for those partners which form strongly bound intermediates, suggesting that this specific electronic channel is controlled by different regions of the potential energy surfaces.

Original languageEnglish
Pages (from-to)542-553
Number of pages12
JournalJournal of Physical Chemistry A
Issue number4
Publication statusPublished - 3 Feb 2005


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