State-resolved collisional quenching of highly vibrationally excited pyridine by water: The role of strong electrostatic attraction in V→RT energy transfer

Abstract

We report experiments that investigate the influence of long-range attractive forces on collisional energy loss from highly vibrationally excited molecules. State-resolved studies of energy transfer from highly vibrationally excited pyridine (μ=2.2 D) to water (μ=1.8 D) in a low-pressure environment at 298 K have been performed using high-resolution transient absorption spectroscopy of water at λ≈2.7 μm. Pyridine in its ground electronic state with 37 900 cm−1 of vibrational energy was prepared by absorption of pulsed ultraviolet light (λ=266 nm) to the S1 state, followed by rapid internal conversion to the S0 state. Collisions between vibrationally excited pyridine and water that result in rotational and translational excitation of the ground vibrationless state of H2O (000) were investigated by monitoring the populations of individual rotational states of H2O (000) at short times following pyridine excitation. The infrared probe of water was the highly allowed asymmetric stretching (000→001) transition. The nascent distribution of rotationally excited H2O (000) states is well described by a thermal distribution with a rotational temperature of Trot=770±80 K. Doppler-broadened transient linewidth measurements yield the velocity distributions of the recoiling H2O (000) molecules that correspond to center-of-mass translational temperatures of Ttrans∼515 K for all water rotational states investigated. Additionally, rate constants for energy gain in individual water states were determined, yielding an integrated rate constant of k2int=1.1×10−11 cm3 mol−1 s−1 for the appearance of H2O (000) with Erot=1000–2000 cm−1. These results are compared with previous relaxation studies of excited pyrazine (μ=0 D) with water and of excited pyridine with CO2 (μ=0 D), and the influence of electrostatic attraction on the relaxation dynamics is discussed.

Full State-Resolved Energy Gain Profiles of CO2 (J = 2−80) from Collisions of Highly Vibrationally Excited Molecules. 1. Relaxation of Pyrazine (E = 37900 cm−1)

“…53,54 Supercol- lision dynamics were first characterized by Flynn and coworkers for the pyrazine(E):CO 2 system using transient IR absorption. 34,35 The Mullin group has investigated supercollision dynamics for a number of highly excited donor molecules (pyrazine, pyridine, alkylated pyridines, and azulene) with a range of bath molecules (CO 2 , H 2 O, HOD, and DCl) 42,43,45,46,[55][56][57][58] and investigated the energy dependence of supercollisions for pyrazine(E), pyridine(E), and azulene(E) with CO 2 . 40,41,44,59,60 Sevy and co-workers have studied the interplay of photodissociation dynamics with collisional deactivation for several donor molecules with CO 2 .…”

Classical Trajectory Study of Energy Transfer in Pyrazine−CO Collisions

“…In this paper, we describe preliminary results on vibrationally excited pyrazine colliding with a different cold bath gas, CO; a more complete experimental paper is in preparation . Using similar teclmiques, Mullin and co-workers − have studied pyrazine/CO 2 , , pyrazine/H 2 O, pyridine/CO 2 , and pyridine/H 2 O . They have paid particular attention to the dependence of the energy loss on the initial excitation energy.…”

Energy Transfer Dynamics in the Presence of Preferential Hydrogen Bonding: Collisions of Highly Vibrationally Excited Pyridine-h5, -d5, and -f5 with Water

“…Each data set was fit to a Boltzmann distribution with a rotational temperature. The distribution of scattered water from pyridine-h 5 was measured to be T rot ) 890 ( 150 K. This result is slightly larger than, but within error of, our previous result of T rot ) 770 ( 80 K. 19 For collisions of water with pyridined 5 , the scattered H 2 O(000) has a rotational temperature of T rot ) 890 ( 90 K, which is similar to the result for pyridine-h 5 : H 2 O. Less rotational energy is imparted to the high-J states of water in collisions with pyridine-f 5 where the rotational temperature of scattered water is T rot ) 530 ( 55 K.…”

“…19 A sensitive test of large-∆E collisions between vibrationally hot molecules and a 300 K bath is the nascent rotational temperature, T rot , of scattered bath molecules. Earlier studies on a series of pyridine-based donors have shown that T rot for scattered H 2 O(000) molecules (with E rot > 1000 cm -1 ) decreases systematically for donors that have larger size, more vibrational modes, and increased vibrational state density.…”