Dennis J. Clouthier

A pyrolysis jet spectroscopic study of the rotationally resolved electronic spectrum of dichlorocarbene

The rotationally resolved, gas phase vibronic spectrum of dichlorocarbene has been recorded using the technique of pyrolysis jet spectroscopy. The rovibronic analysis has established the band origin of the A 1B1–X 1A1 electronic transition to be at 17 255.67 cm−1. The observed vibrational frequencies in the ground and excited states are very close to published values from matrix isolation data. The excited state structure has a 131.4° ClCCl angle and a 1.652 A CCl bond length.

Asyrotwin: A 32-bit Windows version of Asyrot, A program for the analysis of high resolution singlet-singlet band spectra of asymmetric tops

Abstract A new version of the Asyrot program has been written to extend the computational limits to J=999 and K a =450 and to include the octic, M K , and N K centrifugal distortion constants. The number of transitions calculated and fitted is limited only by available computer memory. Two new phases have been added to the program so that the parameters of a single state can be refined by forming combination differences and then fitting them, along with any available microwave lines, to the appropriate Hamiltonian. A new Windows interface has been integrated with the Fortran code to greatly facilitate the editing of the input data. A limited Windows based band contour plotting and comparison feature has been added. Two utility features are also available. The first allows for the easy transfer of observed line frequencies to the corresponding transition quantum labels listed in the input file. The second allows for the summation of several calculated spectra, of different bands or isotopomers, into an overall contour which can be compared to an observed spectrum.

REINVESTIGATION OF THE HSICL ELECTRONIC SPECTRUM : EXPERIMENTAL REEVALUATION OF THE GEOMETRY, ROTATIONAL CONSTANTS, AND VIBRATIONAL FREQUENCIES

The ground and first excited singlet states of monochlorosilylene have been reexamined using pulsed discharge jet and laser induced fluorescence techniques. HSiCl and DSiCl have been produced by an electric discharge through SiHCl3 and SiDCl3 vapor in argon. The 000 band rotational constants of four isotopomers of HSiCl and the harmonic force fields for both states have been combined to obtain the following estimates of the equilibrium structures: r′′(SiCl)=2.067(3) A, r′′(SiH)=1.525(5) A, θ′′(HSiCl)=96.9(5)°, r(SiCl)=2.040(3) A, r(SiH)=1.532(8) A, and θ(HSiCl)=118.1(5)°. Previous anomalies in the ground-state structure and the excited-state vibrational frequencies have been resolved. The radiative lifetime of the 480–400 nm (A 1A′′–X 1A) band system of HSiCl has been measured to be 432±20 ns.

Resolution of anomalies in the geometry and vibrational frequencies of monobromosilylene (HSiBr) by pulsed discharge jet spectroscopy

A detailed examination of the ground and first excited singlet electronic states of HSiBr has been carried out through analysis of the 500–400 nm band system, using pulsed discharge jet and laser‐induced fluorescence techniques. HSiBr and DSiBr have been produced by an electric discharge through SiHBr3 and SiDBr3 vapor in argon. Rotational analysis of the 000 bands yielded the structural parameters r0″(SiH)=1.518(1) A, r0″(SiBr)=2.237(1) A, θ0″=93.4(3)°, r0′(SiH)=1.497(10) A, r0′(SiBr)=2.208(2) A, and θ0′=116.4(7)°. Previous anomalies in the geometric parameters and vibrational frequencies have been resolved and the ground state bond lengths and vibrational frequencies are found to be comparable to those of SiH and SiBr. Harmonic force fields have been determined for the ground and excited states and the radiative lifetime of HSiBr has been measured to be 598±18 ns.

Pyrolysis jet spectroscopy

Abstract Pyrolysis jet spectroscopy, in which precursor species are heated to pyrolysis temperatures just prior to expansion from the nozzle of a supersonic free jet, is demonstrated to be a viable technique for the production and characterization of rotationally cold transient molecules and free radicals.

High-resolution pulsed dye laser calibration in the 500-350 nm region using iodine atlas reference lines

A simple, inexpensive method for precisely calibrating high resolution, pulsed dye lasers in the 500–340‐nm wavelength region has been devised. The residual portion of the laser beam exiting from an experiment is Raman shifted to longer wavelnegths in a high‐pressure hydrogen cell. The Stokes shifted output is used to excite laser induced fluorescence (LIF) signals in I2 vapor, which, in turn, are used to accurately calibrate the wavelength of the Raman shifted beam. The constant Raman shift, which can be precisely calculated, is then added to give the original laser wavelength. The method is readily adapted to computerized data acquisition and gives results of comparable accuracy to those of I2 LIF calibrations in the conventional 850–500 nm region.

The electronic spectrum, molecular structure, and oscillatory fluorescence decay of jet-cooled germylidene (H2C=74Ge), the simplest unsaturated germylene

The electronic spectrum of germylidene (H2C=Ge), the simplest unsaturated germylene, has been observed for the first time. Jet-cooled H2CGe and D2CGe were produced by an electric discharge through tetramethylgermane diluted in argon at the exit of a supersonic expansion. High-resolution spectra of H2C74Ge and D2C74Ge, obtained from (CH3)474Ge prepared from isotopically enriched 74Ge metal, have been rotationally analyzed to yield the following r0 structures: r0″(CGe)=1.7908(2) A, r0″(CH)=1.1022(5) A, θ0″(HCH)=115.05(5)°, r0′(CGe)=1.914(4) A, r0′(CH)=1.082(9) A, and θ0′(HCH)=139.3(11)°. The 367–354 nm B1B2–X 1A1 band system consists of prominent perpendicular bands involving the CGe stretching (ν3) and CH2 scissors (ν2) vibrations and a weaker series of vibronically induced parallel bands involving the CH2 rocking mode (ν6). Vibronic bands involving Δv=2 changes in ν6(b2) and ν4(b1) have also been assigned. The fluorescence decays of single rotational levels of the 000 band of H2C74Ge exhibit molecular q...

Jet spectroscopy, structure, anomalous fluorescence, and molecular quantum beats of silylidene (H2C=Si), the simplest unsaturated silylene

The jet-cooled B 1B2–X 1A1 spectrum of silylidene, the simplest unsaturated silylene, has been observed for the first time. H2C=Si and D2C=Si have been produced by an electric discharge through tetramethylsilane and tetramethylsilane-d12 vapor diluted in argon at the exit of a supersonic expansion. Rotational analysis of the 000 bands yielded the following substitution structures: rs″(CSi)=1.706(5) A, rs″(CH)=1.099(3) A, θs″(HCH)=114.4(2)°, rs′(CSi)=1.815(5) A, rs′(CH)=1.073(4) A, and θs′(HCH)=133.7(1)°. The electronic transition consists primarily of strong electronically allowed perpendicular bands, but a weaker system of vibronically induced parallel bands has also been assigned. Transitions involving Δv=2 changes in the ν6 (b2) mode show up prominently in the spectrum, due to a very large change in the vibrational frequency on excitation. Silylidene has very interesting excited state decay dynamics. Anomalous S2−S0 fluorescence is observed due to the very large S2−S1 energy gap. Rotational level spe...

The rotational spectrum of CuCCH(X̃ Σ1+): A Fourier transform microwave discharge assisted laser ablation spectroscopy and millimeter/submillimeter study

The pure rotational spectrum of CuCCH in its ground electronic state (X̃  (1)Σ(+)) has been measured in the frequency range of 7-305 GHz using Fourier transform microwave (FTMW) and direct absorption millimeter/submillimeter methods. This work is the first spectroscopic study of CuCCH, a model system for copper acetylides. The molecule was synthesized using a new technique, discharge assisted laser ablation spectroscopy (DALAS). Four to five rotational transitions were measured for this species in six isotopologues ((63)CuCCH, (65)CuCCH, (63)Cu(13)CCH, (63)CuC(13)CH, (63)Cu(13)C(13)CH, and (63)CuCCD); hyperfine interactions arising from the copper nucleus were resolved, as well as smaller splittings in CuCCD due to deuterium quadrupole coupling. Five rotational transitions were also recorded in the millimeter region for (63)CuCCH and (65)CuCCH, using a Broida oven source. The combined FTMW and millimeter spectra were analyzed with an effective Hamiltonian, and rotational, electric quadrupole (Cu and D) and copper nuclear spin-rotation constants were determined. From the rotational constants, an r(m)(2) structure for CuCCH was established, with r(Cu-C) = 1.8177(6) Å, r(C-C) = 1.2174(6) Å, and r(C-H) = 1.046(2) Å. The geometry suggests that CuCCH is primarily a covalent species with the copper atom singly bonded to the C≡C-H moiety. The copper quadrupole constant indicates that the bonding orbital of this atom may be sp hybridized. The DALAS technique promises to be fruitful in the study of other small, metal-containing molecules of chemical interest.

The electronic spectrum of silicon methylidyne (SiCH), a molecule with a silicon–carbon triple bond in the excited state

The A 2Σ+–X 2Πi transition of jet-cooled silicon methylidyne, SiCH, has been recorded by laser-induced fluorescence in the 850–600 nm region. The radical was produced in an electric discharge using tetramethylsilane as the precursor. Fifteen cold bands of SiCH and 16 bands of SiCD have been assigned vibrationally, giving the upper state frequencies as v2′=715/558 cm−1 and v3′=1168/1127 cm−1 for SiCH/SiCD. Rotational analysis of the 000 and 303 bands for each isotopomer has given the following molecular structures: r0″(Si–C)=1.692 52(8), r0″(C–H)=1.0677(4), r0′(Si–C)=1.6118(1), and r0′(C–H)=1.0625(5) A. The silicon–carbon bond length in the X 2Π ground state of SiCH (electron configuration …σ2π3) is typical for a Si=C double bond; in the A 2Σ+ excited state (…σ1π4) it corresponds to a triple bond. This work provides the first experimental measurement of the length of the carbon–silicon triple bond.