Search

The free radicals, silyl (SiH3) and silylidyne (SiH), play important roles at the gas-surface interface during the chemical vapor deposition (CVD) of silicon films from silane, SiH4. We will report recent experiments that enable resonance enhanced multiphoton ionization (REMPI) spectroscopy to detect these radicals with great sensitivity. These newly developed REMPI detection methods should allow experimentalists to measure the relative concentration profile of SiH3, SiH, and Si radicals in the same experimental configuration and under the same conditions. For the SiH3 radical the new spectra will also permit temperature measurements.

The mass‐resolved, one‐color, 2+1 resonance‐enhanced multiphoton ionization (REMPI) spectrum of the BF radical between 304 and 337 nm is reported and rotationally analyzed. The B 1∑+ (3s)←←X 1∑+ origin is observed to have a strong Q branch and much weaker O and S branches. Since they are forbidden in one photon, these rotational branches have not been previously observed. This is the first REMPI study of any boron‐containing radical. We find that 2+1 REMPI is a convenient method for the detection of boron monofluoride, having sensitivity better than 108 cm−3.

The one-color, 2+1 resonance-enhanced multiphoton ionization (REMPI) spectrum of boron atoms ( 2p P2j∘) is studied between 304 and 350 nm. The most intense peak is at 346.10 nm for 4p P2J∘ ←←2p P23/2∘. The recorded spectrum includes a new np Rydberg series. We report laser wavelengths and new atomic energy levels and suggest 2+1 REMPI as a convenient method for the detection of atomic boron.

The reactions of F(2P)+ketene and F(2P)+ketene‐d2 were studied in a flow reactor. Spectra of the radical products CH2F, CD2F, CH, CF, and atomic carbon were detected between 292–395 nm by resonance enhanced multiphoton ionization (REMPI) mass spectrometry. Fluoromethyl radicals were identified as a major product of the F+ketene elementary reaction. REMPI spectra of fluoromethyl radicals originated from two‐photon preparation of 3p, 4p, and 5p Rydberg states (quantum defect ∼0.6). Absorption of a third laser photon ionized the radicals, a 2+1 REMPI mechanism. Rydberg band origins were observed in CH2F at ν00=52 863, 63 275, and 67 265 cm−1 and in CD2F at ν00=52 786, 63 195, and 67 186 cm−1. A normal mode analysis revealed the vibrational frequencies of the C–F stretch, CH2 scissors, and out‐of‐plane bending modes in the Rydberg states. The ground state out‐of‐plane bending frequency in CH2F is 260(30) cm−1 and in CD2F it is 170(30) cm−1. CH radicals were generated by the photolysis of ketene and observed a...

We report the resonance enhanced multiphoton ionization spectra of ClO and BrO free radicals between 415 and 475 nm. The observed electronic states were prepared by simultaneous absorption of three identical photons from a dye laser. Absorption of at least one additional photon induced ionization. ClO showed spectra originating from the D, E, and F states previously reported by N. Basco and R. D. Morse. The origin of the F 2Σ←X 2Πi bands were reassigned to ν00=70 183 cm−1 and ν00=69 868 cm−1. BrO showed three new vibrational progressions originating from transitions between the X 2Π3/2 state to Rydberg states with assignments of E 2Σ (ν00=65 003 cm−1), F 2Σ (ν00=67 470 cm−1), and an apparently inverted state, designated G (ν00=70 504 cm−1), that possesses orbital angular momentum greater than zero. The G‐state bands were separated by 139(±3) cm−1 which should approximate the magnitude of the spin‐orbit coupling constant of this excited state if it is of 2Πi symmetry.

The technique of arrested relaxation infrared chemiluminescence has been utilized for the observation of emission from the polyatomic substitution products of fluorine atom reactions with ethylene, propene, vinyl chloride, and vinyl bromide. A new apparatus for performing such experiments is described. The entire apparatus, including the scanning Michelson interferometer used in obtaining the emission spectra, is cooled to liquid nitrogen temperatures or lower. The resulting improvement in signal to noise ratio allows emission spectra to be recorded down to frequencies as low as 720 cm−1. Analysis of the chemiluminescence data allows the determination of the partitioning of reaction energy over the product vibrational modes. The results indicate statistical partitioning occurs for the vinyl chloride and bromide reactions, while the ethylene and propene reactions exhibit nonstatistical partitioning. The difference in energy partitioning for these reactions is attributed to the existence of a potential energy barrier in the exit channel for the latter two reactions, while no such barrier exists for the former reactions.

We report the resonance enhanced multiphoton ionization spectrum of SiF between 430 and 492 nm. SiF radicals absorbed at least three photons to generate the observed m/z 47 SiF ions. Two-photon absorption bands from C″ 2 Σ + ← X 2 Π, and C′ 2 Π ← X 2 Π, transitions were observed. An intense band from sequential one-photon transitions from the X 2 Π 1/2 (υ″ = 0) state through the A 2 Σ + (υ′ = 0) and C″ 2 Σ + (υ′ = 1) states was observed.

The resonance enhanced multiphoton ionization (REMPI) spectra of CH2OH, CH2OD, CD2OH, and CD2OD between 420–495 nm are reported. Analysis of the excited state vibrational band progressions shows that the spectrum originates from simultaneous two photon absorption to form a 3p Rydberg state (ν00=40 064 cm−1) of the radical. Absorption of a third photon ionized the radical. A normal mode analysis of the REMPI spectra enabled assignments of six active vibrational modes in the excited state. The no isomerization of methoxy radicals into hydroxymethyl radicals was observed. The experimental measurement uncertainty limits this isomerization rate to less than 2.9 s−1 at 300 K.

The germyl (GeH3) radical has been observed by resonance enhanced multiphoton ionization (REMPI) spectroscopy in the region of 370–430 nm. The spectrum arises from two‐photon resonances with the 5p 2A‘2 (D3h) Rydberg state that possesses an origin at 419.1 nm (ν0–0 =47 705 cm−1). A vibrational progression of 756 cm−1 was assigned to the ‘‘umbrella’’ mode, ν2. The observed X 2A1 (C3v) v‘2=2 to v‘2=0 vibrational interval is 663 cm−1 which leads to an estimated barrier to inversion of 1530 cm−1.

The resonance enhanced multiphoton ionization (REMPI) spectrum of O2 a 1Δg between 305 and 350 nm is reported. The spectrum is compared to the REMPI spectrum of ground state molecular oxygen in the same electronic energy region, and a number of differences in the respective spectra are observed. Detection limits for O2 a 1Δg by REMPI is calculated to be 5×109 molecule cm−3 in the ion source of the mass spectrometer.