Collisional effects in the multiphoton absorption processes of chloroform-d

Abstract

The multiphoton absorption and decomposition of CDC13 induced by TEA-C02 laser pulses have been studied at low pressures of CDC13 (0.3 Torr) and with the addition of CHC13 and Ar as bath gases. The laser absorption cross section was also measured as a function of incident fluence in the range 0.01-0.7 J/cm1 2. The reaction probability per pulse was measured at fluences of 7-60 J/cm2 as was the effect of added CHC13 and Ar at 20 and 33 J/cm2. The experimental results were modeled with a master equation with explicit consideration of rotational and anharmonic bottlenecks. The calculations in the high-pressure region allowed obtainment of information about the energy transferred by collision of the vibrationally excited CDC13 with CHC13 and Ar. An energy-dependent value of <A£)d produces the best fit to the experimental results.

Collisional Deactivation of CDCl3 Excited with a TEA CO2 Laser

“…1,14 Under our present experimental conditions, the decomposition of vibrationally excited CDCl 3 (reaction 4) can be neglected. 1 The experimental results were used to obtain information on the energy transfer process due to collisional relaxation of vibrationally excited CDCl 3 with Ar or in self-collisions. Different approaches were used.…”

“…As expected for a small molecule such as CDCl 3 , 〈n〉 increases with the pressure of added inert gas up to a fluence dependent limiting value at pressures above ∼40 Torr, due to collisional relaxation of the rotational and anharmonic bottlenecks to absorption. 1,15 The processes undergone by a CDCl 3 molecule irradiated by a CO 2 laser in the presence of Ar, as deactivating gas, can be represented by the following scheme:…”

“…These values of 〈∆E〉 d , for both Ar and CDCl 3 , are in good agreement with those obtained by the direct and the inversion methods, but they are smaller than those extracted from model calculations involving molecules excited above the reaction threshold. 1 All the results obtained are compared in Table 1.…”

The IR multiphoton decomposition of CF3I. The effect of inert and reactive gases

“…Further evidence for this behavior comes from the pressure dependence of the reaction probability, which shows the typical enhancement upon the addition of small amounts of bath gas and goes through a maximum at pressures where the effect of vibrational deactivation compensates the rate of rotational hole filling. Model calculations on CDC13 [30] and CDF3, [12,17l indicate that at total pressures above this maximum yield, the fraction of molecules interacting with the laser is unity, that is, all the rotational and anharmonic restrictions to absorption have been collisionally removed and the molecule assumes the behavior of a large molecule.…”

“…The inconvenience of dealing with a bimodal distribution of absorbing molecules in model calculations with the master equation formulation has been well documented [12,30]. For this reason, the experiments subject to modelling were all performed under conditions where the restrictions imposed by the rotational bottleneck have been relaxed, which implies experiments with the addition of at least 1 torr of isobutane.…”