Daniel K. Havey

A comparison of experimental and calculated spectra of HNO3 in the near-infrared using Fourier transform infrared spectroscopy and vibrational perturbation theory

This work combines new laboratory studies of the near-infrared vibrational spectra of HNO3 with theoretical predictions of these spectra as a means to understand the properties of this molecule at energies well above the fundamental region. Trends in overtone and combination band energy levels and intensities are compiled and examined. The theoretical calculations are in excellent agreement with the observed frequencies and intensities of the transitions in this spectral region. The calculations also serve as a valuable aid for assigning many of the transitions. This work validates the ab initio generated potential energy surface for HNO3 by comparing vibrational perturbation theory calculations to experimental spectra focused on combination band and overtone absorptions.

Experimental Line Parameters of the b^(1)Σ^(+)_g ← X^(3)Σ^(-)_g Band of Oxygen Isotopologues at 760 nm Using Frequency-Stabilized Cavity Ring-Down Spectroscopy

Positions, intensities, self-broadened widths, and collisional narrowing coefficients of the oxygen isotopologues 16O18O, 16O17O, 17O18O, and 18O18O have been measured for the b1 Sigma(g) + <-- X3 Sigma(g) - (0,0) band using frequency-stabilized cavity ring-down spectroscopy. Line positions of 156 P-branch transitions were referenced against the hyperfine components of the 39K D1 (4s 2S1/2 --> 4p 2P1/2) and D2 (4s 2S1/2 --> 4p 2P3/2) transitions, yielding precisions of approximately 0.00005 cm-1 and absolute accuracies of 0.00030 cm-1 or better. New excited b1 Sigma(g) + state molecular constants are reported for all four isotopologues. The measured line intensities of the 16O18O isotopologue are within 2% of the values currently assumed in molecular databases. However, the line intensities of the 16O17O isotopologue show a systematic, J-dependent offset between our results and the databases. Self-broadening half-widths for the various isotopologues are internally consistent to within 2%. This is the first comprehensive study of the line intensities and shapes for the 17O18O or 18O2 isotopologues of the b1Sigma(g) + <-- X3 Sigma(g) - (0,0) band of O2. The 16O2, 16O18O, and 16O17O line parameters for the oxygen A-band have been extensively revised in the HITRAN 2008 database using results from the present study.

Full state-resolved energy gain profiles of CO2 from collisions with highly vibrationally excited molecules. II. Energy-dependent pyrazine (E = 32,700 and 37,900 cm(-1)) relaxation.

The full state-resolved distribution of scattered CO2 (00(0)0) molecules from collisions with highly vibrationally excited pyrazine (E = 32,700 cm(-1)) is reported and compared to previous studies on pyrazine (E = 37,900 cm(-1)) to investigate how internal energy content impacts the dynamics for collisional quenching of high energy molecules [J. Phys. Chem. A 2010, 113, 1569]. Nascent rotational and translational energy profiles for scattered CO2 (00(0)0) molecules with J = 2-72 were measured using high-resolution transient infrared absorption and combined with earlier results for the J = 56-78 states [J. Chem. Phys. 1999, 111, 7373]. The product translational energy for individual J-states increases by 50% for a 16% increase in donor vibrational energy. The nascent rotational distribution for scattered CO2 is biexponential, comprising 77% nearly elastic collisions and 23% inelastic collisions. The spread of the rotational distribution is sensitive to donor energy, but the branching ratio for elastic and inelastic collisions is the same for both donor energies. The measured collision rates are close to the Lennard-Jones values and are only weakly dependent on changes in donor energy. The nascent energy gain distribution function P(ΔE) depends strongly on the energy, and this energy dependence is stronger than the linear dependence seen in multicollision energy transfer studies for pyrazine(E) + CO2 collisions.

Energy transfer dynamics in the presence of preferential hydrogen bonding: collisions of highly vibrationally excited pyridine-h5, -d5, and -f5 with water.

The relaxation of highly vibrationally excited pyridine-h5, pyridine-d5, and pyridine-f5 (E approximately 38,000 cm(-1)) through collisions with water was investigated by high resolution transient IR absorption spectroscopy to investigate how preferential hydrogen bonding interactions impacts the energy transfer dynamics. Nascent rotational and translational energy gain profiles for scattered H2O(000) molecules with E(rot) > 1000 cm(-1) are reported. H2O(000) molecules scattered from pyridine-h5 and pyridine-d5 have rotational distributions with T(rot) = 890 K. Less rotational energy is found in H2O(000) scattered from pyridine-f5 for which T(rot) = 530 K. The recoil energy distributions are similar for the three donors with T(rel) = 400-700 K. To explain the results, a torque-inducing mechanism is proposed that involves directed movement of water between sigma and pi-hydrogen bonding interactions with the pyridine donors. The experimental results are consistent with this mechanism, and with effects due to the state-density energy dependence of the highly excited donor molecules. Differences in vibrational mode frequencies of the hot donor molecules do not appear to explain the experimental results.

Spectroscopic Measurement of the Vapour Pressure of Ice

We present a laser absorption technique to measure the saturation vapour pressure of hexagonal ice. This method is referenced to the triple-point state of water and uses frequency-stabilized cavity ring-down spectroscopy to probe four rotation–vibration transitions of at wavenumbers near 7180 cm−1. Laser measurements are made at the output of a temperature-regulated standard humidity generator, which contains ice. The dynamic range of the technique is extended by measuring the relative intensities of three weak/strong transition pairs at fixed ice temperature and humidity concentration. Our results agree with a widely used thermodynamically derived ice vapour pressure correlation over the temperature range 0°C to −70°C to within 0.35 per cent.

Effects of alkylation on deviations from Lennard-Jones collision rates for highly excited aromatic molecules: collisions of methylated pyridines with HOD.

Collision rates and energy transfer distributions are reported for HOD with highly vibrationally excited 2-methylpyridine (2-picoline, E = 38 310 cm(-1)) and 2,6-dimethylpyridine (2,6-lutidine, E = 38 700 cm(-1)). High resolution transient IR absorption is used measured to complete product state distributions of scattered HOD(000) molecules with E(rot) = 109 to 1331 cm(-1). Doppler-broadened line profiles characterize the depletion and appearance for HOD molecules due to collisions with hot donors and show that the product translational and rotational energy distributions are similar for both donors with DeltaE(rel) = 370 cm(-1) and DeltaE(rot) approximately 75 cm(-1). The energy transfer rate for picoline (E)/HOD is 2.5 times larger than the Lennard-Jones collision rate. The energy transfer rate for lutidine(E)/HOD is 3.2 times larger than the Lennard-Jones collision rate. Previous work ( Havey, Liu, Li, Elioff, and Mullin, J. Phys. Chem. A 2007, 111, 13321-9 ) reported similar energy transfer values for pyrazine/HOD collisions and an energy transfer rate that is 1.7 times the Lennard-Jones collision rate. The observed collision rates are discussed in terms of hydrogen bonding interactions between HOD and the aromatic donor molecules. Energy gain profiles for HOD are compared with those for H(2)O.