Frank T. Prochaska

Matrix photodissociation and photoionization of carbon tetrahalides with noble gas resonance radiation

Experiments have shown that the coaxial orifice discharge tube is an effective windowless resonance lamp for argon and neon photolysis of matrix‐isolated molecules. Argon resonance photoionization of CCl4 produced CCl+3 at 1037 cm−1, which photolyzed with intense visible light. Discharged noble gas mixtures produced increased yields of CCl3 and CCl2 and new bands sensitive to near‐infrared photolysis, which are assigned to the weakly‐bound species CCl+3–Cl, CCl2–Cl+2, and Cl+3. Krypton resonance photoionization of CBr4 gave CBr+3 at 874 cm−1, which also decreased with intense mercury arc photolysis.

Vibration–rotational and pure rotational laser–Raman spectra of H2, D2, and HD in matrices at 12 K

The vibration–rotational and pure rotational laser–Raman spectra of H2, D2, and HD were observed in argon, krypton, xenon, nitrogen, and oxygen matrices at 12 K. Transitions arising from the J=0 and J=1 rotational levels were seen for H2 and D2, but from only the J=0 level for HD. Only transitions from the J=0 level were observed for H2 in an oxygen matrix. It is interesting that hydrogen is trapped at all in an inert gas matrix at 12 K; this indicates that hydrogen molecule–inert gas atom interactions are stronger than hydrogen–hydrogen interactions.

Matrix radiolysis and photoionization of CF2Cl2 and CF3Cl. Infrared spectra of CF2Cl+ and the parent cations

The ’’Freon’’ molecules CF2Cl2 and CF3Cl have been subjected to matrix radiolysis and photoionization during condensation with excess argon at 15 K. Infrared spectra showed stable and free radical products and new absorptions due to charged species. The molecular ion bands exhibited different behavior on filtered mercury arc photolysis. New 1415 and 1515 cm−1 absorptions decreased by 220–1000 nm photolysis are assigned to CF2Cl+2 and CF3Cl+. Other absorptions eliminated by mercury arc light, some of which were produced on photolysis of sodium–chlorofluoromethane samples, are attributed to molecular anions. The vibrational assignments were verified by carbon‐13 isotopic studies.

Matrix radiolysis and photoionization of CFCl3. Infrared spectra of CFCl+2 and the parent cation

The ’’Freon’’ compound CFCl3 has been subjected to radiolysis and photoionization during condensation with excess argon at 15 K. Infrared spectra of the matrix samples identified stable and free radical products and new absorptions which are attributed to charged species. The molecular ion bands exhibited three different behavior patterns on filtered mercury arc photolysis: The most photosensitive bands, destroyed by 420–1000 nm light, are assigned to the parent cation; several absorptions which photodissociated with 290–1000 nm radiation are due to a molecular anionic species; and new bands reduced by 220–1000 nm light are assigned to the daughter cation CFCl+2. The vibrational assignments were confirmed by carbon‐13 substitution.

Infrared spectra of the CH2F2+, CHF2+, CHF+, and FH– (CHF)− molecular ions in solid argon

Argon resonance photoionization of argon–methylene fluoride samples during condensation at 15 K produced three groups of new infrared absorptions, which are separated by their mercury arc photolysis behavior and isotopic data. Four infrared absorptions assigned to CH2F2+ correspond closely with CH2F2 neutral absorptions both in position and carbon‐13 and deuterium shifts. The C–H stretching modes of CH2F2+ are lowered by the removal of a C–H bonding electron. The high antisymmetric C–F2 stretching fundamental for CHF2+ at 1608 cm−1 is consistent with extensive pi bonding in this planar cation. A sharp 1368 cm−1 absorption is attributed to the C–F stretching mode of CHF+. Strong, broad absorptions showing small carbon‐13 shifts are assigned to the H–F stretching and hydrogen deformation modes of the intramolecular hydrogen bonded electron‐capture product (F–H) –– (CHF)−. A vibronic absorption from 413 to 544 nm in these samples is attributed to the CHF intermediate.

Vacuum-ultraviolet photoionization of bromoform and its chlorine substituted counterparts during condensation with argon at 15 K: Infrared spectra of the (CHX2+)X and X−-HCX2 molecular ions

Abstract Samples of bromoform, bromoform-d and the chlorine substituted counterparts were deposited onto a 15 K cold window during simultaneous irradiation from an open microwave discharge of argon. Infrared absorptions previously assigned to daughter cations and anions showed a 2 to 10 cm −1 dependence on the detached chlorine or bromine atom, which appears to be trapped in the same matrix cage with the molecular fragment. Spectroscopic considerations favor the (CHX 2 + )X and X − -HCX 2 identifications for these ionic species. Subsequent photolysis with the filtered light of a mercury arc selectively destroyed these ions and produced CX 3 , CX 3 + , and Ar n H + or Ar n D + upon rearrangement with the detached halogen atom.

Infrared spectra of the CHFCl, CHFBr, and CHFI free radicals in solid argon

Abstract Lithium atom matrix reactions with CHFCl 2 , CHFBr 2 , and CHFI 2 produced new infrared absorptions due to the lithium halides LiX and the CHFX free radicals. The CHFCl assignments are supported by 13 C and D isotopic substitution, and the CHFBr and CHFI radical absorptions were also found in CH 2 FBr and CH 2 FI photolysis studies. The CHFX, CHF 2 , and CHX 2 radical fundamentals are compared.