Infrared Laser Stark Spectroscopy of Methyl Fluoride in He Nanodroplets.

We measured the rotationally resolved infrared spectra of helium solvated methyl fluoride at 3 μm and 10 μm, wherein lies C-H and C-F stretching bands, respectively. The linewidths (FWHM) were found to increase with increasing vibrational energy and range from 0.002 cm in the v band (C-F stretch) at ~1047 cm, to 0.

Laser Spectroscopy of Helium Solvated Clusters of Methanol and Methanol-Water in the Symmetric Methyl Stretching Band.

Mid-infrared spectra of methanol and methanol-water clusters have been investigated in the symmetric CD stretching band of CDOH and CDOD. We find that the position of this band provides a useful signature of the general type of hydrogen-bonded cluster it is associated with. Our results are consistent with those previously reported in the OH stretching region (Sulaiman, M.

Characterization of the Coriolis Coupled Far-Infrared Bands of -Vinyl Alcohol.

Rotational emission from vibrationally excited molecules are responsible for a large fraction of lines in the spectra of interstellar molecular clouds. Vinyl alcohol (VA) has two rotamers that differ in energy by 6.4 kJ/mol, both of which have been observed toward the molecular cloud, Sagittarius B2(N) [Turner and Apponi, 2001, 561, 207].

Laser spectroscopy of helium solvated molecules: probing the inertial response.

Helium is the only solvent within which molecules can "freely" rotate, albeit with an increased moment of inertia relative to the gas phase. Evidence for this can be obtained by performing infrared laser spectroscopy on molecules embedded large helium clusters (nanodroplets), which often reveals rotationally resolved lines that are more closely spaced than . The additional rotational inertia results from coupling of the helium to the molecule (rotor), and decreases in going from heavy (, SF) to light (, CH) rotors due to a partial breakdown in the adiabatic (following) approximation; faster (lighter) rotors cannot couple as well to helium since their effective interaction with helium is less anisotropic.

Observation of the elusive "oxygen-in" OCS dimer.

The carbonyl sulfide (OCS) dimer serves as a prototype system for studying intermolecular forces between nonsymmetrical linear polyatomic molecules. Here, we performed a laser spectroscopic investigation of OCS dimers embedded in helium nanodroplets and found rovibrational bands corresponding to the non-polar "sulfur-in" and parallel polar dimers that have been extensively characterized in the gas phase, as well as a new non-polar "oxygen-in" dimer that has long been predicted by theory. Frequency alternations in the rotational branches along with the absence of a Stark effect provided important clues as to its assignment.

Far-Infrared Synchrotron Spectroscopy of a Potentially Important Interstellar Isotopologue of Vinyl Alcohol: CHCHOD.

The far-infrared spectrum (100-500 cm) of a isotopologue of the astrophysically important molecule, vinyl alcohol, is reported. We observed several low energy (OD) torsional bands: the fundamental and first two hot bands of the rotamer and the fundamental and first hot band of the (higher energy) rotamer. While the bands corresponding to the rotamer are somewhat obscured by rotational lines of water (making a full spectroscopic analysis unfeasible at this stage), the -vinyl alcohol bands are not, and a global fit was performed that included 4404 distinct infrared lines assigned in this work, in addition to 59 previously reported microwave lines.

Laser Spectroscopy of Methanol Isotopologues in He Nanodroplets: Probing the Inertial Response around a Moderately Light Rotor.

High-resolution, mid-infrared spectra of methanol isotopologues (CHOH, CHOD, CDOH, and CDOD) embedded in superfluid helium nanodroplets have been obtained. For the normal isotopologue, we observed the CO stretching overtone band, the lines within which are 2× broader than in the fundamental for E species methanol and no different than the fundamental for A species methanol. For CHOD, we observed the CO stretching overtone band for the first time, which was characterized by narrow line widths for both nuclear spin species.

Far-Infrared Synchrotron Spectroscopy and Quantum Chemical Calculations of the Potentially Important Interstellar Molecule, 2-Chloroethanol.

The high brightness of the Australian synchrotron allowed for detailed spectra to be collected at high resolution (0.00096 cm) in the vicinity of the a/ b/ c-type ν band of 2-chloroethanol, which involves O-H torsional motion about the C-O bond. A rovibrational analysis was performed for both chlorine isotopologues in the ν fundamental (centered at ∼344 cm) which involved the assignment of 7153 lines ( J ≤ 90, K ≤ 41).

Quantum cascade laser spectroscopy of OCS isotopologues in He nanodroplets: A test of adiabatic following for a heavy rotor.

We report high-resolution infrared spectra of OCS isotopologues embedded in helium nanodroplets that were recorded with a newly built spectrometer. For the normal isotopologue, we observed the relatively weak third bending overtone band, in addition to new high J transitions in the C-O stretching fundamental, which has previously been investigated by diode laser spectroscopy [S. Grebenev et al.

Infrared Spectroscopy of the Entrance Channel Complex Formed Between the Hydroxyl Radical and Methane in Helium Nanodroplets.

The entrance channel complex in the exothermic OH + CH → HO + CH reaction has been isolated in helium nanodroplets following the sequential pick-up of the hydroxyl radical and methane. The a-type OH stretching band was probed with infrared depletion spectroscopy, revealing a spectrum qualitatively similar to that previously reported in the gas phase, but with additional substructure that is due to the different internal rotation states of methane (j = 0, 1, or 2) in the complex. We fit the spectra by assuming the rotational constants of the complex are the same for all internal rotation states; however, subband origins are found to decrease with increasing j.

Rotational Spectroscopic Study of Quantum Solvation in Isotopologic (pH)-CO Clusters.

We report the Fourier transform microwave spectra of (pH)-CO, (pH)-CO, and (pH)-CO (N ≤ 8) clusters. We find that the frequencies of the a-type J = 1-0 transitions decrease to a minimum at N = 6 and then rapidly increase up to at least N = 8; this is similar to what was previously reported for (pH)-CO, for which the turnaround was found to correlate with an increase in the superfluid fraction of the pH component of the clusters [ Raston Phys. Rev.

Infrared Stark and Zeeman spectroscopy of OH-CO: The entrance channel complex along the OH + CO → trans-HOCO reaction pathway.

Sequential capture of OH and CO by superfluid helium droplets leads exclusively to the formation of the linear, entrance-channel complex, OH-CO. This species is characterized by infrared laser Stark and Zeeman spectroscopy via measurements of the fundamental OH stretching vibration. Experimental dipole moments are in disagreement with ab initio calculations at the equilibrium geometry, indicating large-amplitude motion on the ground state potential energy surface.

Mid-infrared signatures of hydroxyl containing water clusters: Infrared laser Stark spectroscopy of OH-H2O and OH(D2O)n (n = 1-3).

Small water clusters containing a single hydroxyl radical are synthesized in liquid helium droplets. The OH-H2O and OH(D2O)n clusters (n = 1-3) are probed with infrared laser spectroscopy in the vicinity of the hydroxyl radical OH stretch vibration. Experimental band origins are qualitatively consistent with ab initio calculations of the global minimum structures; however, frequency shifts from isolated OH are significantly over-predicted by both B3LYP and MP2 methods.

Microwave spectroscopy of the seeded binary and ternary clusters CO-(pH2)2, CO-pH2-He, CO-HD, and CO-(oD2)(N=1,2).

We report the Fourier transform microwave spectra of the a-type J = 1-0 transitions of the binary and ternary CO-(pH2)2, CO-pH2-He, CO-HD, and CO-(oD2)N=1,2 clusters. In addition to the normal isotopologue of CO for all clusters, we observed the transitions of the minor isotopologues, (13)C(16)O, (12)C(18)O, and (13)C(18)O, for CO-(pH2)2 and CO-pH2-He. All transitions lie within 335 MHz of the experimentally or theoretically predicted values.

Infrared rovibrational spectroscopy of OH-C2H2 in (4)He nanodroplets: Parity splitting due to partially quenched electronic angular momentum.

The T-shaped OH-C2H2 complex is formed in helium droplets via the sequential pick-up and solvation of the monomer fragments. Rovibrational spectra of the a-type OH stretch and b-type antisymmetric CH stretch vibrations contain resolved parity splitting that reveals the extent to which electronic angular momentum of the OH moiety is quenched upon complex formation. The energy difference between the spin-orbit coupled (2)B1 (A″) and (2)B2 (A') electronic states is determined spectroscopically to be 216 cm(-1) in helium droplets, which is 13 cm(-1) larger than in the gas phase [Marshall et al.

Liquid hot NAGMA cooled to 0.4 K: benchmark thermochemistry of a gas-phase peptide.

Vibrational spectroscopy and helium nanodroplet isolation are used to determine the gas-phase thermochemistry for isomerization between conformations of the model dipeptide, N-acetylglycine methylamide (NAGMA). A two-stage oven source is implemented to produce a gas-phase equilibrium distribution of NAGMA conformers, which is preserved when individual molecules are captured and cooled to 0.4 K by He nanodroplets.

Single and double resonance spectroscopy of methanol embedded in superfluid helium nanodroplets.

Methanol is one of the simplest molecules that undergo torsional oscillations, and so it has been extensively studied in the gas phase by various spectroscopic techniques. At 300 K, a large number of rotational, torsional, and vibrational energy levels is populated, and this makes for a rather complicated spectrum, which is still not fully understood. It is expected that in going from 300 K to 0.

High-resolution infrared spectroscopy of atomic bromine in solid parahydrogen and orthodeuterium.

This work extends our earlier investigation of the near-infrared absorption spectroscopy of atomic bromine (Br) trapped in solid parahydrogen (pH2) and orthodeuterium (oD2) [S. C. Kettwich, L.

Helium nanodroplet isolation and infrared spectroscopy of the isolated ion-pair 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

The ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide was vaporized at 420 K, and the ion-pair constituents were entrained in a beam of liquid He nanodroplets and cooled to 0.4 K. The vapor pressure was optimized such that each He droplet picked up a single ion-pair from the gas phase.

The ethyl radical in superfluid helium nanodroplets: rovibrational spectroscopy and ab initio computations.

The ethyl radical has been isolated and spectroscopically characterized in (4)He nanodroplets. The band origins of the five CH stretch fundamentals are shifted by < 2 cm(-1) from those reported for the gas phase species [S. Davis, D.

Infrared spectroscopy and tunneling dynamics of the vinyl radical in 4He nanodroplets.

The vinyl radical has been trapped in (4)He nanodroplets and probed with infrared laser spectroscopy in the CH stretch region between 2850 and 3200 cm(-1). The assigned band origins for the CH2 symmetric (ν3), CH2 antisymmetric (ν2), and lone α-CH stretch (ν1) vibrations are in good agreement with previously reported full-dimensional vibrational configuration interaction computations [A. R.

Anomalous Λ-doubling in the infrared spectrum of the hydroxyl radical in helium nanodroplets.

The X(2)Π3/2 hydroxyl (OH) radical has been isolated in superfluid (4)He nanodroplets and probed with infrared laser depletion spectroscopy. From an analysis of the Stark spectrum of the Q(3/2) transition, the Λ-doublet splittings are determined to be 0.198(3) and 0.

Rotational dynamics of the methyl radical in superfluid 4He nanodroplets.

We report the ro-vibrational spectrum of the ν3(e') band of the methyl radical (CH3) solvated in superfluid (4)He nanodroplets. Five allowed transitions produce population in the N(K) = 0(0), 1(1), 1(0), 2(2) and 2(0) rotational levels. The observed transitions exhibit variable Lorentzian line shapes, consistent with state specific homogeneous broadening effects.

Infrared spectroscopy of HOOO and DOOO in 4He nanodroplets.

The HOOO hydridotrioxygen radical and its deuterated analog (DOOO) have been isolated in helium nanodroplets following the in situ association reaction between OH and O(2). The infrared spectrum in the 3500-3700 cm(-1) region reveals bands that are assigned to the ν(1) (OH stretch) fundamental and ν(1) + ν(6) (OH stretch plus torsion) combination band of the trans-HOOO isomer. The helium droplet spectrum is assigned on the basis of a detailed comparison to the infrared spectrum of HOOO produced in the gas phase [E.