Articles you may be interested inRotationally resolved spectroscopy of the A ̃ A 2 1 ← X ̃ B 2 1 transition of H 2 S + above the barrier to linearity using the mass-analyzed threshold ionization photofragment excitation technique Using the technique of double-resonance overtone photofragment spectroscopy ͑DROPS͒, we have measured rotationally resolved vibrational overtone transitions to the previously unobserved 5v 1 , 6v 1 , and 7v 1 levels of gas-phase trans-nitrous acid ͑HONO͒ in its electronic ground state. Observing the onset of dissociation from different rovibrational states of 5v 1 near threshold determines the HO-NO bond energy to be D 0 ϭ16 772Ϯ14 cm Ϫ1 . Observed spectral splittings and broadening of individual rovibrational transitions provide quantitative data on the rate and extent of collision free vibrational energy redistribution that would result after coherent ultrashort pulse excitation. In parallel with these frequency domain measurements, we determine the unimolecular dissociation rates directly in time for trans-HONO molecules excited to several rotational states near threshold. The combination of time-and frequency-resolved data allows us to estimate the linewidth contributions from the finite dissociation lifetime of the molecule. Our results reveal intramolecular dynamics that are clearly not a simple function of the vibrational energy but rather depend sensitively upon specific couplings and, in turn, on the vibrational character of the individual states excited.

Loosely bound states of jet cooled NO 2 just below the first dissociation threshold D 0 , with binding energies E b between 0.8 and 59.3 cm -1 , have been investigated using pulsed VIS/UV optical double resonance spectroscopy. The measured UV spectra of these states in a spectral region where free NO absorbs have been found to depend strongly on the binding energy E b ) D 0 -E. This suggests that the states just below the dissociation threshold D 0 may be regarded (at least in part) to belong to a family of states corresponding to a large amplitude motion of an "oxygen atom" and a "NO fragment". Such states, typical for loosely bound nonrigid molecules or van der Waals complexes, are unusual for chemically bound molecules. In this paper we are describing first experiments in which we obtained direct evidence for their existence in NO 2 . Most of the absorptions from the loosely bound states terminate on a dissociative potential energy surface (PES), so that the corresponding spectrum is a broad unstructured feature, with a blue shift (compared to free NO) increasing with binding energy. Very weak bound-bound transitions have also been observed. The analogy to spectra of NO/Ar van der Waals complexes is discussed.

Linewidths, unimolecular dissociation rates and product state distributions (PSDs) have been measured for single rovibratational states of the ν1=5–7 levels of gas-phase trans-nitrous acid (HONO) by double-resonance overtone photofragment spectroscopy (DROPS). The linewidth measurements, together with the unimolecular dissociation rates in 5ν1, suggest that the intramolecular dynamics are not statistical but rather depend sensitively upon specific intramolecular couplings and the vibrational character of the initial state. Comparison with calculated rate constants from statistical unimolecular rate theory reveals that intramolecular vibrational energy redistribution (IVR) is the rate determining step in the dissociation of HONO subsequent to vibrational overtone excitation. Despite this, we find the measured product state distributions to be close to the predictions of statistical theory. We explain these observations in terms of a simple tier model incorporating hierarchical IVR. The experimental findings underscore the importance of the preparation technique, and hence the nature of the initially excited state, in determining the subsequent intramolecular dynamics.

Articles you may be interested inRotationally specific rates of vibration-vibration energy exchange in collisions of NO (X 2 Π 1/2 ,v=3) with NO (X 2 Π,v=0) J. Chem. Phys. 111, 9296 (1999); 10.1063/1.479843 State-resolved collisional quenching of highly vibrationally excited pyridine by water: The role of strong electrostatic attraction in V→RT energy transfer J. Chem. Phys. 111, 3517 (1999); 10.1063/1.479635State-resolved collisional energy transfer in highly excited NO 2 . I. Cross sections and propensities for J, K, and m J changing collisions A combined experimental and theoretical study of rotational energy transfer in collisions between NO (X 2 Π 1/2 , v=3,J) and He, Ar and N 2 at temperatures down to 7 K State-resolved collisional relaxation of highly vibrationally excited pyridine by CO 2 : Influence of a permanent dipole moment

Articles you may be interested inVibrational and rotational energy transfers involving the CH B Σ − 2 v = 1 vibrational level in collisions with Ar, CO, and N 2 O Rotationally specific rates of vibration-vibration energy exchange in collisions of NO (X 2 Π 1/2 ,v=3) with NO (X 2 Π,v=0) J. Chem. Phys. 111, 9296 (1999); 10.1063/1.479843State-resolved collisional energy transfer in highly excited NO 2 . II. Vibrational energy transfer in the presence of strong chemical interaction A combined experimental and theoretical study of rotational energy transfer in collisions between NO (X 2 Π 1/2 , v=3,J) and He, Ar and N 2 at temperatures down to 7 K State-resolved collisional relaxation of highly vibrationally excited pyridine by CO 2 : Influence of a permanent dipole moment