Multiphoton absorption and decomposition studies of chloroform-d induced by a pulsed ¹³CO₂ laser

Abstract

The multiphoton absorption (MPA) and decomposition (MPD) of chloroform-d induced by various "CO, [00°1 4 10°0] lines were studied for pressures from 0.133 to 13.3 kPa. MPA results show a cross-section increasing with pressure up to a plateau value which is likely due to rotational hole-filling. A MPA "spectrum" of the average number of photons absorbed versus wavenumber for different "CO, laser lines is shifted to lower wavenumbers compared to the small signal absorption spectrum by at least 5 cm-' suggesting that a small amount of anharmonicity bottle-necking is occurring in CDCI,. A comparison of the MPD probability versus fluence for CDCI3 with that measured by other workers for fluoroform indicates that the CDC13 is decomposed at a slightly lower fluence by an appropriate line of a pulsed CO, laser.For the pressure range (0.2 to 4.0 kPa) and laser pulse-width used, the MPD is second order in CDCI,. The primary decomposition channel is elimination of DCI followed by reaction of CCI, to give CzCIZ, C2C4, and CI,. The DCI produced exchanges with a source of H,O in the reaction cell to give significant quantities of HCI. A post-pulse reaction between (HCI + DCI) and C2CI2. produces (CrDC13 + C,HCl3). Significant quantities of CCI, are also produced by undetermined reactions.

Direct determination of the dissociation probability in highly focused IR multiple photon dissociation

“…The saturation fluence corresponds to the fluence value for which half the CDCl 3 molecules within the observation region are dissociated. The value of Φ sat obtained is consistent with the values reported by other authors in different experimental conditions [17,18]. The excellent agreement between the In order to prove this hypothesis, we carried out experiments to determine the global dissociation probability per pulse from the measurement of the fraction of molecules dissociated per pulse by infrared spectrometry.…”

Infrared multiphoton decomposition of highly excited t‐butyl chloride‐d9

“…The PSE method was first applied to CDC13 [ll. At the fluence studied, the dominant term in the expansion was h20 (positive) confirming previous findings [8] that collisional up-pumping processes (sometimes called energy pooling) could be more important than pressure-independent MPD (designated by hlo [5,91). One of the product molecules from CDC13 dissociation, CZC14, absorbed the laser radiation, and a positive hll indicated that it was contributing this energy to the decomposition of the CDC13 molecules through collisional energy transfer.…”

Decomposition of highly vibrationally excited CDCl3

“…10.1 1.5 In other experiments in this laboratory, decomposition under similar conditions was second order. 2 Isotope selectivity for CTCl 3 has been observed 9 • 11 • 1O with high separation factors in decomposition of mixtures with CDCl 3 and this appears most compatible with time-dependent first-order ki-.) Also at: National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario, Canada KIA OR6 b) Dr. Robert A.…”