Double-resonance overtone photofragment spectroscopy of trans-HONO. I. Spectroscopy and intramolecular dynamics

Abstract

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.

The infrared-driven cis–trans isomerization of nitrous acid HONO III: A mixed quantum–classical simulation

“…Apparently, the excited OH-stretching mode and the torsional mode (i. e. the reaction coordinate) are efficiently coupled. Presumably, the coupling is mediated by the matrix, as this reaction has not been reported in the gas-phase so far [8]. The molecule is extremely well characterized by vibrational and electronic spectroscopy [8][9][10][11][12][13][14][15][16][17][18].…”

“…On the picosecond timescale, the molecule does not dissipate energy into the environment, nevertheless, environment fluctuations are crucial for relaxation and isomerization to occur. It is stressed again that the reaction does not occur in the gas phase [8,[19][20][21][22]. Environment fluctuations are needed to produce curvecrossings and to redistribute population between adiabatic eigenstates, but this is done without inreversibly exchanging energy with the environment.…”

“…Presumably, the coupling is mediated by the matrix, as this reaction has not been reported in the gas-phase so far [8]. The molecule is extremely well characterized by vibrational and electronic spectroscopy [8][9][10][11][12][13][14][15][16][17][18]. Furthermore, because of its small size, the molecule is particularly suited for theoretical studies on the absolutely highest conceivable level [19][20][21][22], and therefore has prototype character.…”

“…The matrix seems to be crucial for the reaction to occur [8]. In the present paper, the realms of the two worlds are combined by performing a mixed quantum-classical simulation that treats the hydrogen atom as a quantum particle and the ONO-body as well as the matrix environment as classical.…”

Intramolecular vibrational energy relaxation in nitrous acid (HONO)

“…[8][9][10] The HONO system has been studied intensively both theoretically 6,7,[11][12][13][14][15][16][17][18][19][20][21][22][23] and experimentally. [3][4][5][24][25][26][27][28][29] Neither experimental 30 nor theoretical 12,20 studies could find the reaction taking place in the gas phase with significant yields; hence, isomerization seems to be facilitated by the dissipative forces of the matrix environment. In this context we decided to investigate the isomerization of HONO in the time domain with the help of ultrafast IR pump-probe spectroscopy.…”