Rotational energy levels of the three isotopologues of water, for E < 150 cm−1. Levels are labelled by . Ortho levels (H2O, K a + K c odd; D2O, K a + K c even) are depicted in dashed lines.
Schematic of the cross beam VMI setup showing two molecular beams crossing at the center of imaging ion optics.
Experimental setup for normal- to para-H2 conversion.
Raw HDO+ image, showing the molecular beam and laser geometry in the laboratory and center of mass frame. The presented HDO+ image is a 2D projection of the Newton sphere formed by HDO collisions with normal-H2, for the 000 → 111 transition. “CM” refers to the position of the center of mass vector. Forward direction of scattering is defined by the direction of HDO molecules before collision in the center of mass frame.
Comparison of experiment and theory for DCS for HDO scattered by low temperature H2 (T = 200 K nozzle). Theory, red; experimental, black. Normal-H2, full lines. Para-H2, dashed lines. DCSs for para-H2 are divided by 10 for clarity. The HDO rotational transition is indicated in each panel. We use log scales to magnify the small disagreement between experiment and theory in the sideways and backward directions.
Same as Fig. 5 , but room temperature H2 (T = 320 K nozzle).
Comparison of experiment and theory for DCS of D2O scattered by room-temperature normal-H2. Experiment, black. Theory(1) (blue line): Only the ground state of the incoming beam is taken into account. Theory(2) (red line): the incoming beam has either 20% of level 111 (ortho-D2O) or 15% of 110 (para-D2O) in its composition. Both curves are identical for the 101 → 212 transition. We use log scales to magnify the small disagreement between experiment and theory in the sideways and backward directions.
Relative integral cross sections obtained from experiment (black) and quantum mechanical calculations (red) for collisions of HDO with normal-H2 (320 K nozzle). The experimental relative cross sections are normalized to the calculated cross sections at the 111 state. The experimental uncertainty is ∼15%.
Differential cross sections obtained from experiment and theory for collisions of HDO (000-111 transition) with normal-H2 (320 K nozzle). Experiment (1): The DCS of HDO obtained by subtracting the signal due to 111 state population in the HDO beam before collision with H2. Experiment (2): The DCS of HDO without HDO parent beam subtraction. Theory (1) represents the DCS from theory. Theory (2): “Imsim” simulation result of Theory (1) using experimental apparatus function. It gives an estimate of the blurring due to velocity and angular spread in the molecular beams. The angular resolution of the experimental DCSs in the forward direction (0°–30°) is 15°. Normalization is at the values of the DCSs at 60°.
For three isotopologues H2O, HDO, and D2O, comparison of experiment (solid line) and theory (dashed line) for the 000 → 111 transition.
Nozzle and rotational temperatures of H2 molecular beam and the corresponding measured rotational populations.
Total computed cross sections (in Å2, exponent in the parenthesis), for the indicated rotational transitions of HDO colliding with H2. Only observed channels are included. Other values may be obtained from the authors.
Same as Table II , for ortho-D2O and para-D2O transitions. σ o and σ p indicate the total computed cross sections for ortho- and para-D2O, respectively.
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