Philip A. Freedman

NO (C2Π-A2Σ+) emission during the radiative recombination of N and O atoms

Abstract The spectrum of the (0, 0) band in the C 2 Π-A 2 Σ + transition of NO has been observed for the first time at high resolution. The emission arises as a result of recombination of N and O atoms via inverse predissociation. The absence of lines from the lowest lying levels in C 2 Π(υ = 0) fixes the dissociation energy at 52400 ± 10 cm −1 , in excellent agreement with earlier values which were derived indirectly. The break-off in emission is clearly visible in spectra taken from 5 toor of N 2 indicating that N 2 electronically quenches NO C 2 Π(υ = 0) in preference to causing rotational relaxation.

The electronic spectra of argon-tetracene van der waals complexes

Abstract A simple relationship is shown to occur between spectral line position and the number of bound argon atoms in the electronic spectrum of argon-tetracene van der Waals molecules, in contrast to the conclusion of other workers. We show that bonding information may be obtained from such spectra.

The analysis of symmetric rotor Raman spectra: The pure rotational spectrum of 11BF3

Abstract The pure rotational Raman spectrum of 11BF3 has been photographed. Great care was taken in the analysis to consider all the unresolved components under each observed Raman line profile. If this is ignored, systematic errors result. The final set of molecular constants obtained was B0 = 0.34502(±3 × 10−5)cm−1, DJ = 4.38(±0.10) × 10−7cm−1, and DJK = −9.1(±1.0) × 10−7cm−1.

Rotational analysis of the 2A′→2A″ emission band system of HO2 at 1.43 µm

The HO22A′→2A″ emission band at 1.43 µm has been recorded at a resolution of 0.3 cm–1 by use of a SISAM interferometer. Only K′ < 2 levels are found. A full spectroscopic study has been carried out and rotational constants obtained for the 2A′ and 2A″ states, the latter being in agreement with those recently obtained using the laser paramagnatic resonance technique. The 1.51 µm emission and previously assigned to HO2 is found to be due almost entirely to the OH radical.

Determination of the A0 rotational constant for C3v molecules. The ν4 Raman band of methyl iodide

The ν4 Raman band of methyl iodide has been photographed. The data obtained are sufficient to derive an unambiguous value of A0.

Tetracene-argon van der waals molecules

Abstract Expansion of tetracene vapour with excess argon carrier gas through a nozzle of a supersonic jet apparatus permits the controlled formation of (C 18 H 12 )Ar n molecules. These have been studied by laser fluorescence techniques in the 450 nm region of the spectrum corresponding to excitation of the parent tetracene molecules to the 1 B 1u electronic state. We have been able to observe up to the n = 10 complex and have identified three different binding sites on the tetracene framework. From the resolved fluorescence spectra of these species one obtains an upper limit of the van der Waals binding energy of 314 cm −1 in the upper electronic states and 274 cm −1 in the ground state. These resolved spectra also exhibit features identified as due to the tetracene-argon stretching vibration giving a value of 36.5 ± 2 cm −1 for the lowest transition in the ground state of (C 18 H 12 )Ar.

Rotational and vibrational temperatures of naphthalene in a naphthalene-argon supersonic jet

In the A1B2u-X1Ag system of naphthalene in a supersonic jet, rotational contour calculations show rotational temperatures of 2–60 K for argon carrier gas pressures of 1520-120 Torr. The b1u vibration v24 shows a high vibrational temperature which corresponds to the seeding temperature for pressures <400 Torr.

Resonance fluorescence from nitrogen dioxide cooled in a supersonic jet

Abstract Vibrationally resolved resonance fluorescence has been recorded from nitrogen dioxide after excitation in the region 445–460 nm. Emission to v3 = 1 vibrational levels of the ground electronic state is observed in all our spectra.

Rotational Raman spectrum of sulphur dimer

The pure rotational Raman spectrum of S2 has been photographed. After allowance has been made for line blending, the rotational constants obtained were: B0= 0.294 43(± 0.000 05) cm–1 and D0= 19.0(± 0.5)× 10–8 cm–1.

Out-of-plane vibrations of isolated tetracene and pentacene molecules

The electronic spectra of tetracene and pentacene have been studied in a supersonic jet apparatus. Both molecules show excitation to out-of-plane B1g(see-saw) vibrations.