Determination of Nascent H₂ Rovibrational Distributions by Laser Induced Fluorescence: Applications to Formaldehyde Photodissociation and Hydrogen Exchange Reactions

• Main Author: Parker, Garth Rockwood, Jr.
• Format: Others
• Language: en
• Published: 1988
• Online Access: https://thesis.library.caltech.edu/7510/1/Parker_gr_1988.pdf; Parker, Garth Rockwood, Jr. (1988) Determination of Nascent H₂ Rovibrational Distributions by Laser Induced Fluorescence: Applications to Formaldehyde Photodissociation and Hydrogen Exchange Reactions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ht1t-df04. https://resolver.caltech.edu/CaltechTHESIS:03122013-093032947 <https://resolver.caltech.edu/CaltechTHESIS:03122013-093032947>

<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>^rR</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>^rR</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 B&#773; and C&#773; states perturb each other. Attempts to use LIF to study the hydrogen exchange reaction have been unsuccessful.</p>