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The hydroxysilylene (HSiOH) molecule has been spectroscopically identified in the gas phase for the first time. This highly reactive species was produced in a twin electric discharge jet using separate precursor streams of 16O2/18O2 and Si2H6/Si2D6, both diluted in high pressure argon. The strongest and most stable laser induced fluorescence (LIF) signals were obtained by applying an electric discharge to each of the precursor streams and then merging the discharge products just prior to expansion into vacuum. Bands of the Ã1A– X ~ 1A′ electronic transition of HSiOH were found in the 455–420 nm region, and single vibronic level emission spectra showed only transitions attributable to the trans-hydroxysilylene ground state isomer. High resolution, rotationally resolved spectra were obtained for the 0-0 bands of HSi16OH and HSi18OH. The rotational constants were used to obtain ground and excited state molecular structures of HSiOH, with some necessary constraints. The derived ground state structure is trans-HSiOH, with geometric parameters similar to theoretical predictions from the literature. In the excited state, a skew-HSiOH structure was obtained with a dihedral angle of 102°. Our own CASSCF/aug-cc-pVTZ calculations predict a similar excited state skew geometry. The lack of odd quantum number changes in the torsional mode in emission and our difficulties in obtaining DSiOD spectra, despite considerable effort, all suggest that further experimental and theoretical efforts will be necessary to thoroughly understand the electronic spectrum of hydroxysilylene. [ABSTRACT FROM AUTHOR]

GaCH2, a free radical thought to play a role in the chemical vapor deposition of gallium-containing thin films and semiconductors, has been spectroscopically detected for the first time. The radical was produced in a pulsed discharge jet using a precursor mixture of trimethylgallium vapor in high pressure argon and studied by laser-induced fluorescence and wavelength resolved emission techniques. Partially rotationally resolved spectra of the hydrogenated and deuterated species were obtained, and they exhibit the nuclear statistical weight variations and subband structure expected for a 2A2–2B1 electronic transition. The measured spectroscopic quantities have been compared to our own ab initio calculations of the ground and excited state properties. The electronic spectrum of gallium methylene is similar to the corresponding spectrum of the aluminum methylene radical, which we reported in 2022. [ABSTRACT FROM AUTHOR]

The H2CSn and D2CSn molecules have been detected for the first time by laser-induced fluorescence (LIF) and emission spectroscopic techniques through the B ̃ 1 B 2 − X ̃ 1 A 1 electronic transition in the 425–400 nm region. These reactive species were prepared in a pulsed electric discharge jet using (CH3)4Sn or (CD3)4Sn diluted in high-pressure argon. Transitions to the electronic excited state of the jet-cooled molecules were probed with LIF, and the ground state and low-lying A ̃ 1 A 2 state energy levels were measured from single vibronic level emission spectra. We supported the experimental studies by a variety of ab initio calculations that predicted the energies, geometries, and vibrational frequencies of the ground and lower excited electronic states. The spectroscopy of stannylidene (H2CSn) is in many aspects similar to that of silylidene (H2CSi) and germylidene (H2CGe). [ABSTRACT FROM AUTHOR]

The AlCH2 free radical has been spectroscopically identified for the first time. This highly reactive species was produced in an electric discharge jet using trimethylaluminum vapor in high pressure argon as the precursor. The laser-induced fluorescence spectrum of the B ̃ 2 A 2 − X ̃ 2 B 1 band system in the 513–483 nm region was recorded, and the 0–0 bands of AlCH2 and AlCD2 were studied at high resolution. The fine structure splittings were found to be due primarily to the Fermi contact interaction in the excited state rather than the usual spin–rotation coupling. Rotational analysis gave the molecular constants of the combining states, and the geometries were obtained as r ″ A 1 − C = 1.959 1 A ◦ , r ″ C − H = 1.106 1 A ◦ , θ HCH ″ = 110.4 1 ◦ and r ′ A 1 − C = 1.943 1 A ◦ , r ′ C − H = 1.091 1 A ◦ , θ H C H ′ = 115.4 1 ◦ . The bond lengths correspond to an aluminum–carbon single bond in both states. [ABSTRACT FROM AUTHOR]

The divalent tin transient molecules HSnCl and DSnCl have been detected for the first time by laser-induced fluorescence (LIF) spectroscopy. HSnCl/DSnCl were produced in a twin-discharge jet using separate precursor streams of SnH4/SnD4 and the discharge products from HCl/DCl, both diluted in high pressure argon. The A ̃ 1A″– X ̃ 1A′ spectrum of HSnCl consists of a single vibronic 0 0 0 band with a very short fluorescence lifetime (∼30 ns). In contrast, the LIF spectrum of DSnCl exhibits three bands ( 0 0 0 , 2 0 1 , a n d 2 0 2 ), whose fluorescence lifetimes decrease from 393 ns (00) to less than 10 ns (22). Single vibronic level emission spectra have been recorded, providing information on all three vibrational modes in the ground state. Previous detailed ab initio studies indicate that these molecules dissociate into SnCl + H on the excited state potential surface and this is the cause of the short fluorescence lifetimes and breaking off of the fluorescence. It is fortunate that the HSnCl excited state zero-point level is still fluorescent or it would not be detectable by LIF spectroscopy. [ABSTRACT FROM AUTHOR]

The à 2A1– X ̃ 2E electronic transition of the jet-cooled trichlorosiloxy (SiCl3O) free radical has been observed for the first time in the 650–590 nm region by laser induced fluorescence (LIF) detection. The radical was produced by a pulsed electric discharge through a mixture of silicon tetrachloride and oxygen in high pressure argon at the exit of a pulsed molecular beam valve. The LIF spectrum shows low frequency intervals, which we assign as activity in the normally forbidden degenerate v 5 ′ and v 6 ′ modes, indicative of a significant Jahn–Teller effect in the ground state. Single vibronic level emission spectra show level dependent spin–orbit splittings in the ground state and Jahn–Teller predictable variations depending on which upper state level is pumped. The measured lower state energy levels have been fitted to a Jahn–Teller model that simultaneously includes spin–orbit coupling and linear and quadratic multimode coupling. In SiCl3O, the Jahn–Teller interaction predominates over spin–orbit effects. [ABSTRACT FROM AUTHOR]

The A ̃ 2 A 1 − X ̃ 2 B 1 electronic transition of the jet-cooled stibino (SbH2 and SbD2) free radical has been observed for the first time using laser induced fluorescence (LIF) detection. The radicals were produced by a pulsed electric discharge through a mixture of stibine (SbH3 or SbD3) in high pressure argon at the exit of a pulsed molecular beam valve. SbH2 exhibits only three LIF bands, assigned as 2 1 0 , 0 0 0 , and 2 0 1 , with a fluorescence lifetime (τ), which decreases from ∼50 ns for 00 to <10 ns for 21. LIF transitions to the 00 (τ ∼ 2 µs), 21 (τ ∼ 400 ns), and 22 (τ ∼ 75 ns) upper vibronic states of SbD2 were also observed. High-resolution spectra exhibited large spin-rotation splittings and small resolved antimony hyperfine splittings due to a substantial Fermi contact interaction in the excited state. The experimentally determined rotational constants gave effective molecular structures of r 0 ″ = 1.724(2) Å, θ 0 ″ = 90.38(7)° and r 0 ′ = 1.693(6) Å, θ 0 ′ = 120.6(3)°. The ground state bending vibrational levels up to eight quanta (6404 cm−1) in SbH2 and 12 quanta (6853 cm−1) in SbD2 were measured from dispersed fluorescence spectra. All indications are that SbH2 undergoes a dissociative process at low vibrational energies in the excited electronic state. [ABSTRACT FROM AUTHOR]

The SiCF free radical has been spectroscopically identified for the first time. The radical was produced in an electric discharge jet using CF3Si(CH3)3 or CF3SiH3 vapor in high pressure argon as the precursor. The laser-induced fluorescence spectrum of the à ∑ + 2 − X ̃ ∏ 2 band system in the 610 − 550 nm region was recorded and the ∏ 3 / 2 2 spin component of the 0—0 band was studied at high resolution. Rotational analysis gave the B values for the combining states, and by fixing the CF bond lengths at ab initio values we obtained r ″ Si–C = 1. 692 1 Å and r ′ Si–C = 1. 594 ( 1 ) Å. The bond lengths correspond to a silicon-carbon double bond in the ground state and an unusual Si−C triple bond in the excited state. Single vibronic level emission spectra yielded the ground state bending and stretching energy levels. These were fitted to a Renner-Teller model that included spin-orbit and limited vibrational anharmonicity effects. [ABSTRACT FROM AUTHOR]

The SnH2 and SnD2 molecules have been detected for the first time in the gas phase by laser-induced fluorescence (LIF) and emission spectroscopic techniques through the ùB1-X 1A1 electronic transition. These reactive species were prepared in a pulsed electric discharge jet using (CH3)4Sn or SnH4/SnD4 precursors diluted in high pressure argon. Transitions to the electronic excited state of the jet-cooled molecules were probed with LIF, and the ground state energy levels were measured from single rovibronic level emission spectra. The LIF spectrum of SnD2 afforded sufficient rotational structure to determine the ground and excited state geometries: r 0" = 1.768 Å, θ "0 = 91.0°, r0' = 1.729 Å, θ0' = 122.9°. All of the observed LIF bands show evidence of a rotational-level-dependent predissociation process which rapidly decreases the fluorescence yield and lifetime with increasing rotational angular momentum in each excited vibronic level. This behavior is analogous to that observed in SiH2 and GeH2 and is suggested to lead to the formation of ground state tin atoms and hydrogen molecules. [ABSTRACT FROM AUTHOR]

IR–IR double-resonance experiments were used to study the state-to-state rotational relaxation of CO with Ne as a collision partner. Rotational levels in the range Ji=2–9 were excited and collisional energy transfer of population to the levels Jf=2–8 was monitored. The resulting data set was analyzed by fitting to numerical solutions of the master equation. State-to-state rate constant matrices were generated using fitting law functions. Fitting laws based on the modified exponential gap (MEG) and statistical power exponential gap (SPEG) models were used; the MEG model performed better than the SPEG model. A rate constant matrix was also generated from scattering calculations that employed the ab initio potential energy surface of McBane and Cybulski [J. Chem. Phys. 110, 11 734 (1999)]. This theoretical rate constant matrix yielded kinetic simulations that agreed with the data nearly as well as the fitted MEG model and was unique in its ability to reproduce both the rotational energy transfer and pressure broadening data for Ne–CO. The theoretical rate coefficients varied more slowly with the energy gap than coefficients from either of the fitting laws. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An extensive data set of 54 time-resolved pump-probe measurements was used to examine CO+He rotational energy transfer within the CO v=2 rotational manifold. Rotational levels in the range J[sub i]=2–9 were excited and collisional energy transfer of population to the levels J[sub f]=1–10 was monitored. The resulting data set was analyzed by fitting to numerical solutions of the master equation. State-to-state rate constant matrices were generated using fitting law functions and ab initio theoretical calculations that employed the SAPT potential energy surface of Heijmen et al. [J. Chem. Phys. 107, 9921 (1997)]. Fitting laws based on the modified exponential gap (MEG), statistical power exponential gap (SPEG), and energy corrected sudden with exponential power (ECS-EP) models all yielded acceptable simulations of the kinetic data, as did the theoretical rate constants. However, the latter were unique in their ability to reproduce both our kinetic data and the pressure broadening coefficients for CO+He. These results provide an impressive demonstration of the quality of the symmetry adapted perturbation theory (SAPT) potential energy surface. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The vibrational energy levels of the jet-cooled GeCH and GeCD radicals have been studied by a combination of laser-induced fluorescence and wavelength-resolved emission techniques. The radicals were produced in a pulsed electric discharge free jet expansion using methyltrichlorogermane and tetramethylgermane-d[sub 12] precursors. A re-examination of the weaker hot bands in the LIF spectrum has provided a more complete vibrational analysis of the upper state energy levels. The single vibronic level emission spectra obtained by pumping several bands of each isotopomer were analyzed to provide information on the low-lying ground state vibronic energy levels up to 3000 cm-1 above the zero-point level. Strong interactions occur in these molecules between vibronic levels with the same value of P, but differing by one unit of v[sub 2]; such interactions were first described for NCS by Northrup and Sears [Mol. Phys. 71, 45 (1990)] and are conveniently called “Sears resonances.” The spectra of GeCH were further complicated by Fermi resonances between the bending and Ge–C stretching levels. Despite these difficulties, it proved possible to analyze the data using a standard Renner-Teller model with the addition of Sears resonance coupling terms. The validity of the fitted parameters was tested using the isotope relations. The Sears resonance parameters for GeCH are much larger than those of NCS, a result of the much stronger vibronic coupling in the germanium methylidynes. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The electronically forbidden à A[sub 2]-&Xtilde; ¹A[sub 1] band system of jet-cooled silylidene (H[sub 2]CSi and D[sub 2]CSi) has been detected for the first time using laser-induced fluorescence (LIF) and stimulated emission pumping (SEP) techniques. The very weak, vibronically induced 4[sup 1, sub 0] and 3[sup 1, sub 0]4[sup 1, sub 0] bands were detected by LIF along with the corresponding 6[sup 1, sub 0] and 3[sup 1, sub 0]6[sup 1, sub 0] bands which gain intensity through excited state Coriolis coupling. SEP spectra, obtained by pumping the 0[sup 0, sub 0] band of the S[sub 2] state and stimulating transitions down to the S[sub 1] state through the allowed S[sub 2]-S[sub 1] transition, revealed many more bands, including the 0[sup 0, sub 0] bands, which were studied at high resolution and rotationally analyzed. From the upper state rotational constants of H[sub 2]CSi and D[sub 2]CSi, the excited state structure was obtained as r'[sub 0] (SiC)=1.873(2) Å, r'[sub 0](CH)=1.099(5) Å, and θ'[sub 0](HCH)=113.9(3)°. The four lowest energy excited state vibrational frequencies of both isotopomers have also been determined. High level ab initio predictions of the ground and excited state properties of silylidene are also reported and found to be in good agreement with the experimentally determined values. [ABSTRACT FROM AUTHOR]

The laser-induced fluorescence spectrum of the jet-cooled silicon chloromethylidyne (SiCCl) free radical has been identified in the 600-665 nm region. The excitation energy, rotational band contours, vibrational frequencies, and chlorine isotope effects are all consistent with our previous ab initio predictions of the spectroscopic parameters of this radical [J. Chem. Phys. 117, 6439 (2002)]. Single vibronic level emission spectra show an extensive pattern of ground-state vibrational levels which can be assigned to activity in v"[SUB 1] = 1275 cm[SUP-1], v"[SUB 2] = 214.2 cm[SUP-1] and v"[SUB 3] = 528.2 cm[SUP-1]. An analysis of the emission spectra yielded the Renner-Teller parameter ∈ = 0.136(14) and the spin-orbit coupling constant A = -159.4 cm[SUP-1]. The ab initio predictions of the manifold of ground-state vibrational and spin-orbit energy levels were found to be clearly diagnostic, allowing assignments to be made with little ambiguity. [ABSTRACT FROM AUTHOR]

State-to-state rotational relaxation of carbon monoxide (CO) has been studied using an ir double resonance technique. Individual rotational lines of the (2-0) vibrational overtone band were pumped by a pulsed tunable ir laser and the subsequent evolution of the υ=2 rotational population distribution was monitored by the absorption of a tunable cw ir laser via the (3-2) band transitions. Both the excitation and probe lasers were linearly polarized, with linewidths that were narrower than the CO Doppler width. Consequently, alignment and velocity relaxation effects were observed in these measurements. A data set consisting of 54 time-dependent rotational state population profiles was acquired. The full CO-CO rotational relaxation matrix, which consists of state-to-state rate constants for rotational levels up to J=29, was deduced from computer simulations of the data. Scaling and fitting laws were used to provide parametric representations of the rate constants. The three most common models, modified exponential gap, statistical polynomial-exponential gap (SPEG), and energy corrected sudden with exponential-power gap (ECS-EP) were investigated. We concluded that the SPEG law best reproduced the CO-CO rotational energy transfer data. A propensity to preserve the CO parity in rotational energy transfer was observed for collisions where the amount of energy transferred was small. Hence even ΔJ processes were favored for transitions between levels with low Or values. For near-single collisions events a correlation was noted between the amount of rotational energy transferred and the degree of velocity distribution relaxation. This correlation yielded insights regarding the energy transfer dynamics. [ABSTRACT FROM AUTHOR]

Studies the electronic spectrum, molecular structure and oscillatory fluorescence decay of jet-cooled germylidene. Band system; Fluorescence decays of single rotational levels; Density of states; Hyperfine splitting in the Fourrier transform; Occurrence of quantum beats in germylidene.

Laser-induced fluorescence spectroscopy was utilized in the spectroscopic characterization of supersonic expansion-cooled silicon methylidyne. The study, which is also aimed at determining the molecular structure of silicon methylidyne, also resulted in the first-ever detection of germanium methylidyne. Small hydrogen-containing silicon-carbon species, such as SiCH and GeCH, are considered important compounds in both the study of interstellar atmospheres and in the semiconductor industry.