11 research outputs found
Laboratory measurement of the pure rotational spectrum of vibrationally excited HCO^+ (v_2 = 1) by far-infrared laser sideband spectroscopy
Laboratory observations of the pure rotational spectrum of HCO^+ in its lowest excited bending state
(v_1, v^l_2 v_3)_= (0,1^1,0) are reported. Because of their severe excitation requirements, such vibrational satellites
and the high-J ground-state lines also measured here sample only hot, dense regions of matter in active molecular
cloud cores and circumstellar envelopes. As the HCO^+ abundance is tied directly to the gas fractional ionization, it is probable that the vibrationally excited formyl ion transitions will provide high-contrast
observations of shocked molecular material, rather than the more quiescent, radiatively heated gas surrounding
stellar sources detected with the few vibrationally excited neutral species observed to date
Tunable far-infrared laser spectroscopy of hydrogen bonds: The K_a = O(u)â1(g) rotation-tunneling spectrum of the HCI dimer
The ground state K_a =0(u)â1(g) bâtype subband of the rotationâtunneling spectrum of the symmetric ^(35)Clâ^(35)Cl,^(37)Clâ^(37)Cl, and the mixed ^(35)Clâ^(37)Cl hydrogen chloride dimers have been recorded near 26.3 cm^(â1) with subâDoppler resolution in a continuous twoâdimensional supersonic jet with a tunable farâinfrared laser spectrometer. Quadrupole hyperfine structure from the chlorine nuclei has been resolved. From the fitted rotational constants a (H^(35)Cl)_2 centerâofâmass separation of 3.81 Ă
is derived for the K_a =1(g) levels, while the nuclear quadrupole coupling constants yield a vibrationally averaged angular structure for both tunneling states of approximately 20â25 deg for the hydrogen bonded proton and at least 70â75 deg for the external proton. This nearly orthogonal structure agrees well with that predicted by ab initio theoretical calculations, but the observed splittings and intensity alterations of the lines indicate that the chlorine nuclei are made equivalent by a large amplitude tunneling motion of the HCl monomers. A similar geared internal rotation tunneling motion has been found for the HF dimer, but here the effect is much greater. The ground state tunneling splittings are estimated to lie between 15â18 cm^(â1), and the selection rules observed indicate that the trans tunneling path dominates the large amplitude motion, as expected, provided the dimer remains planar. From the observed hyperfine constants, we judge the dimer and its associated tunneling motion to be planar to within 10°
Tunable far infrared laser spectroscopy of van der Waals bonds: Extended measurements on the lowest Sigma bend of ArHCl
A tunable far infrared laser system has been used to measure the vibrationârotation spectrum of the lowest Sigma bending state of ArHCl near 24 cm^â1 in a cw planar jet operating with a terminal jet temperature near 3 K. Over 60 transitions have been observed for both 35Cl and 37Cl isotopes with resolution of the quadrupole hyperfine structure. An improved set of molecular parameters was determined, including B, D, H, and eqQ for both upper and lower states. Very narrow linewidths (approximately 300 kHz) resulting in high resolution and sensitivity make this technique a powerful new method for the detailed investigation of intermolecular forces
Measurement of the perpendicular rotation-tunneling spectrum of the water dimer by tunable far infrared laser spectroscopy in a planar supersonic jet
Fifty-six transitions from the K=1 lower-->K=2 lower tunnelingârotation band of water dimer have been measured and assigned at 22 cm^â1 by direct absorption spectroscopy in a cw planar supersonic jet expansion using a tunable far infrared laser spectrometer. Two different models were used to fit the data and several spectroscopic constants were determined for the upper and lower states. This work supports the local IAM model recently proposed by Coudert and Hougen for the hydrogen bond tunneling dynamics of the water dimer. This model includes four different tunneling motions, all of which contribute to the observed tunneling splittings. This is the most complicated hydrogen bonded system considered to be well understood at this time, at least in the lowest few K states
Tunable far infrared laser spectroscopy of van der Waals bonds: Vibrationârotationâtunneling spectra of ArâH2O
The first high resolution spectra of a rare gasâH2O cluster have been observed using a tunable far infrared laser to probe the vibrationârotationâtunneling levels of ArâH2O formed in a continuous planar supersonic jet. The high sensitivity of this spectrometer facilitated extensive measurements of two perpendicular subbands which are assigned to transitions from the ground state to the upper component of a hydrogen exchange tunneling doublet (c-type) at 21 cm^â1, and to vb1 =1+ (b-type) at 25 cm^â1, the lower tunneling component of a bending vibration which is perpendicular to the tunneling coordinate. The tunneling splitting is shown to be in the range 2.5â7 cm^â1 and the lower tunneling component of the excited bending vibration lies between 39 and 43 cm^â1 above the ground state of the complex. The experimentally determined center-of-mass separation (Rc.m. =3.75 Ă
) and harmonic stretching force constant (ks =0.0134 mdyn/Ă
) are compared to those of related first and second row hydrides. The large amplitude motions occurring within this complex make it difficult to establish its structure
Tunable far infrared laser spectroscopy of van der Waals bonds: Vibrationârotationâtunneling spectra of ArâH 2
Tunable Far Infrared Laser Spectroscopy of Van der Waals Bonds:Extended Measurements on the Lowest ÎŁ Bend of ArHCl
Tunable Far-Infrared Laser Spectroscopy in a Planar Supersonic Jet:The ÎŁ Bending Vibration of Ar-H35Cl
Measurement of the Perpendicular Rotational-Tunneling Spectrum of the Water Dimer by Tunable Far Infrared Laser Spectroscopy in a Planar Supersonic Jet
TUNABLE FAR INFRARED LASER SPECTROSCOPY OF ULTRACOLD FREE RADICALS
We report a new high-resolution spectroscopic technique designed for the study of short-lived free radicals and clusters containing free radicals. Excimer laser photolysis of a suitable precursor during the initial stages of a planar supersonic expansion is used to generate ultracold free radicals which arc subsequently probed by a tunable far infrared laser. A detection limit of lo* molecules/cm3 for light hydrides is demonstrated and prospects for 2 to 3 orders of magnitude improvement are discussed