Determination of Nascent H₂ Rovibrational Distributions by Laser Induced Fluorescence: Applications to Formaldehyde Photodissociation and Hydrogen Exchange Reactions
<p>Individual quantum states of H₂ have been detected using the technique of Laser Induced Fluorescence. This technique is extremely sensitive, with a detection sensitivity of 6 x 10⁸ states cm⁻³ in a probed volume of 0.029 cm³ with a signal-to-noise ratio of 3. This technique is also accurate...
| Summary: | <p>Individual quantum states of H₂ have been detected using the technique of Laser Induced Fluorescence. This technique is extremely sensitive, with a detection sensitivity of 6 x 10⁸ states cm⁻³ in a probed volume of 0.029 cm³ with a signal-to-noise ratio of 3. This technique is also accurate. A spectrum of room temperature H₂ had a rotational temperature of 305.8 ± 3.0 K. LIF detection of H₂ was used to study the H₂CO photodissociation reaction under essentially collision-free conditions. Following excitation of the <i><sup>r</sup>R</i>₃ bandhead of the 2¹₀4³₀ transition at 30388.5 cm⁻¹, the principal product was <i>ortho</i>-H₂. States as high as <i>v</i> = 4, <i>J</i> = 5 were seen. Within the <i>v</i> = 1 channel, the rotational distribution peaked at <i>J</i> = 3. Following excitation of the <i><sup>r</sup>R</i>₄ bandhead of the 2¹₀4³₀ transition at 30396.7 cm⁻¹, the principal product was <i>para</i>-H₂. This is the first report of the <i>para</i>-H₂ distribution following H₂CO dissociation. The rotational distribution is similar to that for <i>ortho</i>-H₂ and peaks at <i>J</i> = 4 within <i>v</i> = 1 channel. This result contradicts a recent theoretical calculation that predicted that the <i>para</i>-H₂ distribution would be bimodal with a minimum at <i>J</i> = 6. Quantitative analysis of higher vibrational levels was hampered by a lack of spectroscopic knowledge (both transition energies and intensities) when the the B̅ and C̅ states perturb each other. Attempts to use LIF to study the hydrogen exchange reaction have been unsuccessful.</p> |
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