The quenching of highly vibrationally excited pyrazine through collisions with CO2 is investigated as a function of initial pyrazine internal energy using a high-resolution laser transient absorption spectrometer. Experiments focus on energy exchanging collisions that result in excitation of rotations and translations in the ground vibrationless (0000) state of CO2. Highly vibrationally excited pyrazine (Evib=37 900 cm−1 or Evib=41 000 cm−1) is prepared via pulsed excitation at 266 nm or 246 nm, followed by rapid radiationless decay to the ground electronic state. The nascent CO2 rotational populations are measured by collecting the transient absorption of individual rovibrational lines at short times following the pyrazine excitation. The translational energies of CO2 recoiling from hot pyrazine are measured for numerous individual rotational levels. Energy dependent rate constants and probabilities are reported for both donor energies and results are compared with earlier studies using 248 nm excitation. These experiments reveal that for both donor energies, significant rotational and translational excitation of CO2 results from collisions with highly vibrationally excited pyrazine, as evidenced by the similarity in the observed rotational and translational distributions. Remarkably, however, the probabilities for the individual energy transfer pathways increase by as much as a factor of 3 for a 7% change in the pyrazine internal energy. The magnitudes and probabilities of energy transfer are described in terms of an energy transfer distribution function for the different donor molecule energies and implications for sequential quenching collisions are discussed.

We report results of the first state-resolved study of large ΔE energy transfer resulting from collisions of highly excited pyrazine with initial vibrational energies of 36000−41000 cm-1. We have used transient infrared absorption spectroscopy to monitor the rotational and translational energy gain in a CO2 bath at short times following collisions with highly excited pyrazine. We have measured nascent distributions of high-energy rotational states, J = 56−84, for CO2 in its ground vibrationless (0000) state, the translational energy gain associated with these excited rotational states, and state-resolved rate constants for excitation of the high-energy bath states. Our results show that for the CO2 rotational states investigated, the nascent rotational distributions and translational energies change very little for a 13% change in pyrazine energy. In contrast, the rate constants for these events are strongly influenced by the donor internal energy content and increase by an order of magnitude for a 5000 cm-1 increase in pyrazine vibrational energy. Our state- and energy-resolved results are compared with experimental measurements of 〈ΔE〉, and implications for the energy dependence of the probability distribution function are discussed.

State-resolved collisional quenching of highly vibrationally excited pyridine by water: The role of strong electrostatic attraction in V→RT energy transfer State-resolved collisional energy transfer in highly excited NO 2 . I. Cross sections and propensities for J, K, and m J changing collisionsThe collisional deactivation of highly vibrationally excited pyrazine by a bath of carbon dioxide: Excitation of the infrared inactive (10 0 0), (02 0 0), and (02 2 0) bath vibrational modes The quenching of highly vibrationally excited pyridine through collisions with a 300 K bath of CO 2 is investigated using high resolution transient infrared laser spectroscopy. Highly excited pyridine (E vib ϭ37 950 cm Ϫ1 ) is prepared using pulsed ultraviolet ͑UV͒ excitation at 266 nm, followed by radiationless coupling to the ground electronic state. Energy gain into CO 2 resulting from collisions with highly excited pyridine is probed using transient absorption techniques. Distributions of nascent CO 2 rotational populations in both the ground (00 0 0) state and the vibrationally excited (00 0 1) state are determined from early time absorption measurements. Translational energy distributions of the recoiling CO 2 in individual rovibrational states are determined through measurement of Doppler-broadened transient line shapes. These experiments investigate the influence of a large permanent dipole moment ( pyridine ϭ2.2 D) on the collisional quenching dynamics of molecules with very large amounts of internal energy. A kinetic model is developed to describe rates for appearance of CO 2 states resulting from collisions with excited pyridine as well as for quenching of excited pyridine at early times. These experiments show that collisions resulting in CO 2 (00 0 0) are accompanied by substantial excitation in rotation ͑T rot ϭ1200 K for Jϭ56-82͒ and translation ͑T trans ϭ2900 K for Jϭ78͒ while the vibrationally excited CO 2 (00 0 1) state has rotational and translational energy distributions near the initial 300 K distributions. Rate constants for the two energy transfer pathways are compared with previously published data on quenching collisions of excited ͑nonpolar͒ pyrazine, revealing only minor relative enhancement ͑ϳ2͒ in the vibrational excitation channel in pyridine relaxation. Overall quenching rates for excited pyridine are determined for both CO 2 states investigated. These data show that the rotational and translational energy gain in CO 2 is much more sensitive to collisional depletion of excited pyridine. This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 131.193.242.44 On: Mon, 01 Dec 2014 21:54:03 k 2 J Pyd(E vib Ϫ⌬E)ϩCO 2 (00 0 0,J,V) and Pyd(E vib ϭ37 950 cm Ϫ1 )ϩCO 2 (00 0 0)→ k 2 J

Energy dependent studies of the collisional relaxation of highly vibrationally excited pyrazine through collisions with CO2 were performed for initial pyrazine energies Evib=31 000–35 000 cm−1. These studies are presented along with earlier results for pyrazine with Evib=36 000–41 000 cm−1. High-resolution transient IR laser absorption of individual CO2 (0000) rotational states (J=56–80) was used to investigate the magnitude and partitioning of energy gain into CO2 rotation and translation, which comprises the high energy tail of the energy transfer distribution function. Highly vibrationally excited pyrazine was prepared by absorption of pulsed UV light at seven wavelengths in the range λ=281–324 nm, followed by radiationless decay to pyrazine’s ground electronic state. Nascent CO2 (0000) rotational populations were measured for each UV excitation wavelength and distributions of nascent recoil velocities for individual rotational states of CO2 (0000) were obtained from Doppler-broadened transient linewidth measurements. Measurements of energy transfer rate constants at each UV wavelength yield energy-dependent probabilities for collisions involving large ΔE values. These results reveal that the magnitude of large ΔE collisional energy gain in CO2 (0000) is fairly insensitive to the amount of vibrational energy in pyrazine for Evib=31 000–35 000 cm−1. A comparison with earlier studies on pyrazine with Evib=36 000–41 000 cm−1 indicates that the V→RT energy transfer increases both in magnitude and probability for Evib>36 000 cm−1. Implications of incomplete intramolecular vibrational relaxation, electronic state coupling, and isomerization barriers are discussed in light of these results.

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Effect of rotation on the translational and vibrational energy dependence of the dissociative adsorption of D2 on Cu(111) J. Chem. Phys. 98, 8294 (1993); 10.1063/1.464535Photoelectron spectroscopy of sulfur atoms produced via twophoton dissociation of sulfur dioxide Correlated rotational and translational product state distributions of the NO X 2 ⌸ 1/2,3/2 ͑vϭ0͒ product of the dissociation of 2-chloro-2-nitrosopropane in a molecular beam following à 1 AЉ←X 1 AЈ͓n͑N͒,*͑Nv0͔͒ excitation at 600 and 650 nm are measured by resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry in a molecular beam. The NO speed distribution appears bimodal and the average speed increases with NO rotational quantum number. The slow component of the NO velocity distribution is attributed to dissociation on the S 0 surface and the fast component to dissociation across a barrier along the reaction coordinate on the T 1 surface. A two-channel dynamical model based on statistical phase space theory is used to model the correlated NO rotational and translational distributions. The experimental data are consistent with a C-N bond energy of 12 900Ϯ200 cm Ϫ1 on the S 0 surface and a barrier height of 1500Ϯ200 cm Ϫ1 on the T 1 surface. The high rotational excitation of NO products originating on the T 1 surface can be attributed to impulsive recoil of NO from a bent C-N-O geometry atop the T 1 barrier.

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