Vibrational energy gain in the v2 bending mode of water via collisions with hot pyrazine (Evib=37900 cm-1):: Insights into the dynamics of energy flow

Energy gain into specific rotational levels of vibrationally excited H2O(010) resulting from collisions with highly vibrationally excited pyrazine in a low-pressure, 298 K environment was investigated using high-resolution transient infrared absorption spectroscopy of water at lambda approximate to 2.7 mum. Vibrationally excited pyrazine with 37900 cm(-1) internal energy was generated by 266 nm optical excitation to an electronically excited singlet state of pyrazine, followed by rapid radiationless decay to the ground electronic state. Collisions between highly excited pyrazine and water that result in excitation of the nu (2) bending vibrational mode (nu (2) = 1594 cm(-1)) in water were studied by monitoring the time-resolved appearance of individual rotational states of cm H2O(010). Transient absorption signals were obtained for a number of rotational states with E-rot less than or equal to 811 cm(-1) The nascent distribution of rotational states for the scattered, vibrationally excited water molecules, H2O-(010), is well characterized by a Boltzmann rotational temperature of T-rot = 630 +/- 90 K. Doppler-broadened transient absorption line shapes for a number of rotational levels within the (010) vibrational state were measured with recoil velocity distributions that correspond to T-trans = 490 +/- 70 K, independent of rotational state. Bimolecular rate constants and Lennard-Jones probabilities for energy transfer into specific quantum states of H2O(010) from collisional deactivation of hot pyrazine were determined as well. Our observations for vibrational energy gain in H2O following collisions with hot pyrazine are compared to earlier studies on collisional energy gain in CO2. The molecular properties of the energy acceptor that influence the relaxation of highly vibrationally excited molecules are explored and insights into the mechanism for vibrational energy gain in water are presented.