Collisional Relaxation of Highly Vibrationally Excited Acetylene Mediated by the Vinylidene Isomer.

Collisional relaxation of highly vibrationally excited acetylene, generated from the 193 nm photolysis of vinyl bromide with roughly 23,000 cm of nascent vibrational energy, is studied via submicrosecond time-resolved Fourier transform infrared (FTIR) emission spectroscopy. IR emission from vibrationally hot acetylene during collisional relaxation by helium, neon, argon, and krypton rare-gas colliders is recorded and analyzed to deduce the acetylene energy content as a function of time. The average energy lost per collision, ⟨Δ⟩, is computed using the Lennard-Jones collision frequency.

Chemical activation through super energy transfer collisions.

Can a molecule be efficiently activated with a large amount of energy in a single collision with a fast atom? If so, this type of collision will greatly affect molecular reactivity and equilibrium in systems where abundant hot atoms exist. Conventional expectation of molecular energy transfer (ET) is that the probability decreases exponentially with the amount of energy transferred, hence the probability of what we label "super energy transfer" is negligible. We show, however, that in collisions between an atom and a molecule for which chemical reactions may occur, such as those between a translationally hot H atom and an ambient acetylene (HCCH) or sulfur dioxide, ET of chemically significant amounts of energy commences with surprisingly high efficiency through chemical complex formation.

Collisional Energy Transfer from Highly Vibrationally Excited Radicals Is Very Efficient.

Although highly vibrationally excited (HVE) radicals are ubiquitous in natural environments, the effect of collisional energy transfer (ET) on their reactivity has yet to be fully characterized. We have used time-resolved IR emission spectroscopy to characterize the vibrational-to-translational quenching of a small HVE radical, ketenyl (HCCO), by inert gases. Photolysis of ethyl ethynyl ether at 193 nm provides HVE HCCO in the X̃(2)A″ electronic ground-state, with a nascent internal energy of 2.

Strong combination-band IR emission from highly vibrationally excited acetylene.

The nu(4) + nu(5) combination band, which appears relatively weak in the IR absorption spectrum, has been identified with exceptionally high intensity in the IR emission spectra from highly vibrationally excited acetylene, which is produced with approximately 71 kcal mol(-1) of vibrational energy from the 193 nm photolysis of vinyl bromide. The 'fundamental' transition of this combination band, from the (0,0,0,1(1),1(-1)) level to the zero point, occurs at 1328 cm(-1). The intensity and frequency of this band as well as the nu(3) and nu(5) bands, IR active but with lower emission intensity, as a function of the acetylene energy can be modeled accurately using the normal mode harmonic oscillator model with frequency anharmonicity corrections.

Vibrational modes of the vinyl and deuterated vinyl radicals.

Following the initial report of the detection of fundamental transitions of all nine vibrational modes of the vinyl radical [Letendre , L. ; Liu , D.-K.

Photodissociation of vinyl cyanide at 193 nm: Nascent product distributions of the molecular elimination channels.

The photodissociation dynamics of vinyl cyanide (H(2)CCHCN, acrylonitrile) and deuterated vinyl cyanide (D(2)CCDCN) at 193 nm are examined using time-resolved Fourier transform infrared emission spectroscopy. Prior photofragment translational spectroscopy studies [D. A.