M. G. Liverman

Rotational analysis of the 1B2u(ππ) ←1A1g, (610) band of benzene and helium–benzene van der Waals complexes in a supersonic jet

The fluorescence excitation spectrum of benzene at a rotational temperature of 0.3 K has been observed using both pulsed and continuously operated supersonic free jets. Individual lines of the 1B2u(ππ) ←1A1g, (610) band at 259 nm have been clearly resolved and analyzed. Rotational and Coriolis constants as derived from these resolved spectra are in agreement with those derived from previous band contour analyses of room temperature spectra. Rotational analyses of the corresponding spectral band for the He–benzene and He2–benzene van der Waals complexes are also reported. In both complexes the helium atoms are found to lie on the C6 symmetry axis approximately 3.5 A above (and/or below) the plane of the benzene ring. Sufficient rotational cooling is achieved in these supersonic expansions so that ≳95% of all benzene molecules are relaxed to the lowest rotational state available (consistent with nonrelaxation of nuclear spins).

Resonance enhanced two‐photon ionization studies in a supersonic molecular beam: Bromobenzene and iodobenzene

The 1B2(ππ*)←1A1 absorptions of two monosubstituted halobenzenes have been investigated using resonance enhanced two‐photon ionization in a pulsed supersonic molecular beam. Detection of the photoions was accomplished by means of a time‐of‐flight mass spectrometer. The 1B2←1A1 system of bromobenzene has been observed with good sensitivity using this technique, even though the total decay rate of the 1B2 state is greater than 1×1011 sec−1. No ion signal was observed when the same transition was probed in iodobenzene, allowing us to place a lower limit on its decay rate of 4×1013 sec−1.

Fluorescence excitation spectrum of the 1Au (nπ) ←1Ag (0–0) band of oxalyl fluoride in a pulsed supersonic free jet

Oxalyl fluoride has been cooled to a rotational temperature of 0.17 K in a pulsed, supersonic jet. Individual rotational lines in the (0–0) band of the fluorescence excitation spectrum have been observed and assigned, and the rotational constants for both the 1Ag and 1Au states have been deduced. The pulsed nozzle used in these experiments can be operated with a far larger orifice diameter and at lower pressures than typically used in continuously operated nozzles, allowing greater cooling and higher jet densities while maintaining a low level of condensation.

Efficient multiphoton ionization of jet-cooled aniline

Abstract Laser excitation of the S 1 ← s o transition in super-cold beams of aniline is found to produce the parent ion with nearly 100% efficiency at a laser flux as low as 2 × 10 7 W cm −2 . Excitation spectra of the photoion signal are similar to the known S 1 ← So absorption spectrum with the addition of power broadening and a non-resonant coherent background.

Rotational and vibrational analysis of the ?←? system of XeF as observed in a supersonic free jet

The fluorescence excitation spectrum of XeF cooled in a supersonic expansion with helium has been observed for the wavelength region 2860 to 3205 A. The cold spectrum displays well‐resolved rotational structure for seven of the XeF isotopic species. Analysis of this rotational structure is reported for v′=16–21 in the ? (Ω=1/2) state and for v″=0 and 1 in the ? 2Σ+ state. Vibrational intervals have been measured for individual XeF isotopes with an accuracy of ±0.50 cm−1 for vibrational levels v′=11–22 and ±0.37 cm−1 for v″=0–2.