Roger Nanes

Rates of collision‐induced electronic relaxation of single rotational levels of SO2 (Ã 1A2): Quenching mechanism by collision complex formation

The electronic quenching cross sections (σQ,M) of SO2 excited to single rotational levels (SRL’s) of the ‘‘B’’ band (J′=9, K′=9) and the ‘‘E’’ band (J′=6, K′=6) were measured from the shortening of the fluorescence decay times by the addition of a variety of nonpolar and polar collision partners (M) at room temperature. σQ,M for the B band SRL varied from 32 A2 for M=He to 863 A2 for M=CH3NO2. A similar variation of σQ,M for the E band SRL was also observed. Eighteen observed values of σQ,M are compared to the values calculated from various theoretical models of electronic quenching including collision complex formation. Temperature dependence of the electronic quenching cross section for the collision complex is presented.

Temperature dependence of intensities of the 8–12 μm bands of CFCl3

Abstract The absolute intensities of the 8–12 μm bands from freon 11 (CFCl 3 ) were measured at temperatures of 294 and 216°K. Intensities of the bands centered at 798, 847, 934, and 1082 cm -1 are all observed to depend on temperature. The temperature dependence for the 847 and 1082 cm -1 fundamental regions is attributed to underlying hot bands; for the ν 2 + ν 5 combination band (934 cm -1 ), the observed temperature dependence is in close agreement with theoretical prediction. The implication of these results on atmospheric i.r. remote-sensing is briefly discussed.

Single rovibronic level lifetimes of the 1A2 state of SO2 excited in the 3043 Å (“E”) band: rotationally resolved fluorescence emission spectrum

Abstract Rotationally resolved resonance fluorescence from selected rovibronic levels of the SO 2 ( 1 A 2 ) molecule has been studied at low pressure. The collision-free lifetime is 13.4±1.3μs. The sum of the cross sections for the collision-induced electronic quenching and “non-specific” rotation-vibration relaxation is ≈480 A 2 .

Band model calculations for CFCl3 in the 8–12 μm region

Abstract A Goody random band model with a Voigt line profile is used to calculate the band absorption of CFCl 3 at various pressures at room and statospheric (216°K) temperatures. Absorption coefficients and line spacings are computed.

Effects of Coriolis interaction on the rotational line intensities of symmetry‐forbidden electronic transitions

The effect of Coriolis coupling on intensities in infrared rotation–vibration bands is here extended to vibronically allowed transitions between electronic states of a nearly symmetric top. Within the framework of the Herzberg–Teller treatment of vibronic interaction, equations are developed which describe the intensity distribution in the p‐ and r‐form branches of a vibronic transition in the cases where Coriolis interaction perturbs one or both vibrational levels associated with the transition. The A 1A2–X 1A1 transition in H2CO is used as an example to illustrate the theory.

SO2 Revisited: laser spectroscopy of cold molecules and collission-induced electronic and rotational relaxation☆

Abstract SO2 has an electronic absorption band in the UV and some of the rotational structures between 3000 and 3300 A have been assigned to the A 1A2← X 1A1 transition by Hamada and Merer (in 1974 - 1975). It is believed that the B 1B1← X 1A1 transition also lies in this wavelength range but extensive perturbations of the B state by the X state have prevented its rotational analysis. In an attempt to locate vibronic origins of two overlapping transitions, we took rotationally resolved fluorescence excitation spectra of cold SO2 molecules (at about 1.0 K) in a supersonic free jet. The rotational structure is greatly simplified and typical vibronic bands consist of from three to five rotational lines, the rRo(O) line being the most intense. Numerous new vibronic features are readily recognized and they make a more precise vibrational assignment possible. In the selective excitation of single rotational levels of the A 1A2 state, the lifetime as well as the intensity distribution of rotationally resolved fluorescence emission were measured as a function of pressure. Collisional electronic quenching by polar molecules is very efficient, reaching a maximum value about 10 times greater than gas kinetic values. Collisional rotational relaxation proceeds by a dipole-type mechanism with a state-to-state cross section of about 50 A2 for ΔKa = +1 or ΔKa = −1.

Long range interaction mechanism for the collision‐induced electronic relaxation of single rotational levels of SO2 (Ã 1A2)

Cross sections for collision induced electronic relaxation of single rotational levels of SO2 (A 1A2) have been measured for a variety of collision partners. Large cross sections (∼10 times the gas kinetic value of ∼80 A2) have been observed. A strong correlation with results from microwave line broadening and rotational relaxation suggest that a long range dipole‐type mechanism is responsible for the efficient electronic quenching. (AIP)