Hot Band Lines Research Articles

New CW CO/sub 2/ laser lines: the 9-μm hot band

We have made what we think is the first observation of the oscillation of the 9-/spl mu/m hot-band lines 01/sup 1/1/spl rarr/[11/sup 1/0,03/sup 1/0]/sub II/ of CO/sub 2/. We have observed 40 lines with a maximum power of 8 W. They will provide a new source of laser radiation for spectroscopy. The set of lines has been positively identified by directly measuring the frequencies of two of the lines with a heterodyne technique using a CO/sub 2/ laser standard.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-resolution spectrum of the C–O stretch overtone band in methyl alcohol

The Fourier-transform spectrum of the CH3OH overtone C–O stretching band (vCO=2←0) has been recorded in the range 1950–2060 cm−1, at a resolution of 0.004 cm−1. The spectrum is resolved into J multiplets, each displaying complicated substructure due to strong torsion–vibration–rotation effects. Within this structure, it has been possible so far to identify R and P branch transitions for K=0 and K=1 for both A and E torsional symmetry species for J≤24. The assignments are supported by combination differences derived from known ground-state frequencies. The identified branches have been analyzed in terms of effective state-dependent series-expansion parameters, and the leading terms in the torsion–rotation Hamiltonian have been derived for the second excited C–O stretching state. The vCO=2 torsional barrier height is obtained as 395.5±0.2 cm−1, and the effective B value as 23 671.9±1.3 MHz. In addition, the 34.946 cm−1 far-infrared laser line pumped by the 10R(48) CO2 laser line has been tentatively identified as the (nτK,J)v=(031+,16)2→(010+,15)2 transition, and its parent IR pump absorption as the P(031+,17) vCO=2←1 hot-band line.

Temperature, Density, and Perturber Dependences of Absorption of the 3.39 µm He–Ne Laser by Methane

We present an experimental and theoretical study of the absorption of the IR He–Ne laser (3.39 µm) by Ch4. Shocktube measurements were made for mixture of CH4 with Ar, N2, and O2 in wide density and temperature ranges. Calculations were made by using the available spectroscopic data on CH4 absorption lines. Comparison between experiments and calculations show that the theoretical predictions are accurate for all densities up to the temperature of 1200 K. At 2000 K, the calculations fail, probably due to insufficient knowledge of hot-band lines. Furthermore, the present study shows that mixture of CH4 with Ar, O2, and N2 lead to absorptions which are similar (within experimental error), as is confirmed by the theoretical model.

Ethylene hot bands from molecular jet double-resonance spectroscopy

Part of the ν10 + ν9 ← ν10 hot-band spectrum, as well as a few lines of the ν7 + ν9 ← ν7 hot band of ethylene, C2H4, have been recorded in a free molecular jet using a double-resonance technique. The identification of the hot-band transitions starting from ν7 has been confirmed in a separate experiment on a (collision-free) molecular beam. Experimentally determined wave-numbers and intensities are given for 169 hot-band lines, 124 of which have been identified. Additional information on symmetry species and rotational energy of the lower levels of a number of as yet unidentified hot-band lines has been obtained from their relaxation behavior. The double-resonance spectra have been confirmed and completed at higher J and Ka values by spectra recorded with a difference frequency spectrometer. The analysis of the ν9 + ν10 state, based on 153 experimentally determined levels, takes into account b-type Coriolis interactions with ν7 + ν11 and ν1 + ν8 states and an anharmonic resonance with the 2ν4 + 2ν8 state, yielding a 0.003 cm−1 standard deviation.

Hot band transition frequencies and line strengths in H 3+: First principles calculations

Ro-vibrational transitions from lower states with one quantum of vibrational energy to upper states with two vibrational quanta, and from lower states with two vibrational quanta to upper states with three, have been calculated from first principles. The calculations make use of the accurate potential energy surface calculated for H 3 + by Meyer, Botschwina, and Burton. The predicted frequencies for the ( v = 2 - v = 1) transitions are reported in excellent agreement with new experimental data and the computed line strengths are consistent with the lines that have been observed. An estimate of the error in the ( v = 3 - v = 2) transitions is ade.

Infrared laser spectroscopy of cations

The high-resolution infrared diode laser absorption spectra of several cations have been recorded and analysed. Most of the spectra were detected with an AC discharge and the velocity-modulation technique, with frequencies up to 60 kHz. In addition to ions, this method can also detect transient neutral species by recording at twice the modulation frequency (concentration modulation). As an example, spectra of an infrared electronic transition in H 2 are described briefly. The diatomic cationic species discussed are CO+ (X 2 E + ) and SH + (X 3 E - ), which are compared with the isoelectronic neutral free radicals CN and PH respectively, also in their ground states. Polyatomic cations that have been studied include HCO+ and H 3 0 + . The bending mode of HCO+ (2) shows a distinctive Q-branch with many resolved components at Doppler-limited resolution and also some hot-band lines. The HCO + spectrum can be combined with microwave measurements in the ground vibrational level to yield predictions for (2 1 ) rotational transitions for astrophysical searches. The most recent spectra of the v 2 ‘umbrella’ mode of H 3 O + , the 2+ &lt;- I - band, provide spectroscopic data on vibrational levels approximately 1000 cm -1 above the inversion potential maximum.

Diode laser measurements of line strengths and widths in the 4.5-μm bands of N 2O

We have made line-strength measurements in the N 2O ν 3-fundamental region using a tunable diode-laser spectrometer. From these measurements and the Herman-Wallis factor determined by Boissy et al., we find the ν 3-fundamental band strength to be S v = 1203 ± 22 cm −2 atm −1 at 297 K. Line-broadening parameters for two ν 3-fundamental lines were determined using nitrogen (N 2) as the broadening gas. Measured strengths and N 2 line-broadening parameters for several ( ν 1 2 + ν 3 − ν 1 2) hot-band lines are also presented.

Detection of SiH(X 2Π) fundamental and hot band transitions by diode laser absorption spectroscopy

Infrared absorption spectra of the SiH free radical have been detected in a silane plasma discharge. In addition to fundamental band transitions some hot band lines have been identified from predictions derived from optical and FTIR data. Low Q-branch transitions in both 2Π1/2 and 2Π3/2 states of the fundamental have been accurately measured and incorporated in a new set of predictions based on the present work and earlier FTIR data.

Line-by-line and narrow-band statistical model calculations for H 2O

In line-by-line calculations we use hot-band lines generated from the AFGL or GEISA data. The parameters of a random statistical model are calculated from these lines for 25 cm -1 wide intervals. Comparisons are made between experimental spectra and results of the two theoretical models for the 1595 and 3755 cm -1 bands between 900 and 1500 K. The validities of the statistical model and of the Curtis-Godson and Lindquist-Simmons approximations for nonisothermal and inhomogeneous media are tested.

Small signal gain measurements for the 00°1–02°0 and 00°1–10°0 bands in a flowing-gas CW CO 2 laser

Small signal gain measurements for a CW flowing-gas CO 2 laser are presented for 43 lines in the 00°1–02°0 band, 45 lines in the 00°1–10°0 band and for quasi-coincidence of the regular band 10P(56) line and 11P(23) line. These results remedy a deficiency in the published literature. Anomalously high gains reported for the first time in a low pressure CW laser on the 10P(20) and 9R(24) lines are attributed to near coincidences with the 11R(23) and 01 11–03 10 R(12) hot-band lines respectively. Using a least-squares fitting procedure, the population inversion ratio is estimated to be between 3 and 7 for the 00°1–02°0 band, and between 4 and 6 for the 00°1–10°0 band. The rotational temperature of the gas is estimated to be 380 ± 5K.

Line assignments and intensities for the ν3 + ν4 − ν4 band of 12CH 4

Assignments and Intensities are reported for 886 lines arising from the “hot-band” ν 3 + ν 4 − ν 4 of 12CH 4 at 3.3 μm. These are determined from spectra at 0.01–0.02 cm −1 resolution that include intensity measurements at reduced temperatures. Energy levels for the v 4 = 1 state through J = 12 are also given based on the ν 3 + ν 4 band assignments of Hunt et al., and the wavenumbers of the hot-band lines.

Electrical and gain characteristics of a multiatmosphere UV-preionized CO&amp;lt;inf&amp;gt;2&amp;lt;/inf&amp;gt;laser

The scaling parameters of a UV-preionized TE CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser which permit the direct comparison of small-signal gains as a function of laser pressure have been investigated in the pressure range of 4-19 atm. Careful measurements of the gain as a function of laser pressure in both the 9.4 and 10.4 μm vibrational bands were made under the appropriate scaling conditions. A theoretical model for the gain incorporating regular, hot band, and sequence band rotational lines, with proper account taken of non-Lorentzian line overlap effects, predicts the observed pressure dependence of the small-signal gain.