Catherine Vermeil

Thermoluminescence following vuv photolysis of OCS and CS2 in an argon matrix

The vuv photodissociation of OCS in an argon matrix at 5 K has been shown to yield S(1S) atoms. The S(1S –1D) emission is observed only during the irradiation and does not appear when CS2 is photolyzed under the same conditions. However, in both cases the thermoluminescence which follows an increase of the matrix temperature is due to the S2(B 3Σu−→X 3Σg−) radiative transition. This substantiates the fact that S atoms do indeed diffuse in an argon matrix already at 6 K. Furthermore, the (a 3Π→X 1Σ+) emission of CS is observed both during the CS2 irradiation and as thermoluminescence. This last observation suggests that C atoms can also diffuse under these conditions at about the same rate as the diffusion rate of N atoms in N2 matrix, measured by Brocklehurst and Pimentel.

Fluorescence and thermoluminescence of N2O, CO, and CO2 in an argon matrix at low temperature

The photolysis of N2O in an argon matrix at 7 °K by 8.4 eV energy photons leads to the emission of the Vegard–Kaplan system of N2 (A 3Σ+→X 1Σ+g) and to the atomic emissions O(1S) →O(1D) and N(2D) →N(4S). The thermoluminescence which accompanies an increase of the matrix temperature is due to O2 (A 3Σ+u→X 3Σ−g). In the presence of CO, the atomic oxygen emission disappears and the CO (a 3Π→X 1Σ) Cameron System is detected. The thermoluminescence in this case is a continuum (3800–5000 A) apparently due to CO2 (3B2→X 1Σ+g) showing that ground state oxygen atoms, O(3P), react with CO at cryogenic temperatures: CO (X 1Σ+)+O(3P) →CO2(3B2), CO2(3B2) →CO2(X 1Σ+g)+hν.

Photolysis of NO trapped in a rigid matrix at 6 K

Nitric oxide embedded in inert solvents has been photolyzed at low temperature (6 K) by different photon energies in the vacuum uv. In argon matrices, two emissions have been identified as the β bands, NO (B 2∏→x 2∏) and as a spin forbidden transition attributed to the M bands. In N2 matrix, only the β bands have been observed. In no case have transitions from Rydberg states been observed.

Emission spectra and radiative lifetimes of the Cameron bands of CO trapped in solid rare gas matrices

The emission spectrum of the Cameron bands (a 3Π→X1 Σ+) of CO molecules trapped in solid Ne, Ar, and Kr has been studied using Xe resonance lamp excitation (λ=147 nm). The lifetime of the a 3Π state has been measured in solid Ne and found to be 90 msec. The decay time of this state is exponential within the range of experimental errors. The lifetime has been calculated assuming spin–orbit mixing between 1Σ+ and 3Π0 states, and found to be 94 msec for J=0. The lifetime values in Ar and Kr matrices are found to be 7.2 and <1 msec, respectively; this is consistent with the matrix shifts in solid Ne, Ar, and Kr, which for the 0–0 bands have been found to be −305, −946, and −2812 cm−1, respectively.

Radiative lifetimes of the b1Σ+ state of NH, ND radicals

Abstract The lifetime of the b 1 Σ + state of the NH radical is measured again and its radiative Einstein coefficient is calculated. By measuring the ND lifetime, and assuming the same Einstein coefficient for both b → X transitions, the nonradiative decay rates are shown to undergo a large isotopic effect. The modes of nonradiative relaxation for the b state are discussed and the isotopic effect is tentatively explained by a rotational coupling with both a and X states. The same mechanism is also thought to be responsible for the large difference between the bimolecular quenching rate constants and for the discrepancy found among previous determinations.

NO+O chemiluminescence in low temperature argon matrix

The far uv photolysis of nitrogen dioxide embedded at 0.1% dilution in an argon rigid matrix at 5 K leads to dissociation into NO+O. When the matrix is warmed up, the atomic oxygen diffuses and a thermoluminescence spectrum is observed corresponding to NO2 emission. This emission is also observed in the thermoluminescence spectrum following the photolysis of NO/O2 (1/1) mixture in the same conditions. It follows that the migration of oxygen in argon matrix is already efficient at 9 K.

Reactions of Hydrogen and Deuterium Atoms Formed in the Photolysis of Methane and Perdeuterated Methane at 123.6 nm

The photolysis of methane and perdeuterated methane has been carried out at 123.6 nm, in the presence of interceptors (deuterium in the case of methane, and hydrogen in the case of deuterated methane). The hydrogen and deuterium atoms formed are statistically in thermal equilibrium with the reaction medium; it follows that the photodissociation into CH3 and H has a probability close to zero at 123.6 nm. In addition, it is confirmed that CH4 and CD4 have different photolytic behaviors insofar as the quantum yields of hydrogen and deuterium are concerned, with φH > φD.

Excited levels of iron, nickel and cobalt obtained by activation of metal carbonyls at 11.8 ev

Abstract When direct or sensitized photolysis of gaseous Fe(CO) 5 , Ni(CO) 4 and CoNO(CO) 3 is carried out with 11.6 and 11.8 cV phoions, all the ligands are removed in a single step; excess energy is removed by the metal atom as electronic excitation. Compared with UV multiphotonic and collision-induced dissociation, the direct pne-phonon photolysis appears to be the most selective excitation method.

Matrix-isolation study of the co2 lowest triplet state

Abstract We have investigated the emission of a CO 2 molecule isolated in an Ar matrix at 4.7 K in the spectral region between 350 and 550 nm. This emission is a continuum with a lifetime of 570 ms. We assign it to the transition from the lowest triplet state (bent) 3 B 2 to the fundamental state (linear) 1 Σ + g .

Nonexponential decay of CS a 3Π–X 1Σ+ luminescence

The VUV photodissociation of CS2 embedded in argon or krypton matrices at 5 K yields to the formation of the CS a 3Π radical. A nonexponential decay of the CS (a→X) emission is observed which can be decomposed into three components. The radiative lifetimes of the 3Π0 and 3Π1 sublevels are calculated. The agreement between experimental and a b i n i t i o values leads to the conclusion that the three spin–orbit sublevels of the CS triplet state decay independently in low temperature matrices.