Matrix isolation spectroscopy of H2O, D2O, and HDO in solid parahydrogen

Transient HDO rovibrational satellite peaks in solid parahydrogen: Evidence of hydrogen atoms or vacancies?

“…This can easily be explained since some of the D 2 O molecules are produced in excited nuclear spin states during photolysis and thus right after photolysis is complete, the intensity of the b-type transition of D 2 O out of the lowest rotational level (0 00 ) increases in intensity as the para-D 2 O molecules in excited rotational levels (1 01 ) convert to the lower energy ortho-D 2 O spin state [1]. Indeed, we have shown in these earlier studies that the growth is first-order with a rate constant consistent with the literature value for the nuclear spin conversion rate constant of D 2 O [1,5]. However, the difference spectrum generated for the analogous b-type HDO rovibrational transition shows a qualitatively different behavior.…”

“…As discussed in the Introduction, this observation confused us in preliminary studies where we speculated the lack of b-type satellite peaks was due either to some sort of selection rules or related to the breadth of the two rovibrational absorptions [1]. These two rovibrational transitions for HDO monomers isolated in solid pH 2 have been well characterized previously [5,24,25], however the reason that the two peaks have such different full width half maximum (fwhm) values has not been considered in detail [5,25]. The greater fwhm of the b-type transition (1.8 cm -1 ) compared to the a-type absorption (0.27 cm -1 )…”

“…The rovibrational bands of asymmetric top molecules such as H 2 O or HDO are classified by whether the transition dipole moment responsible for the absorption has a projection along the A, B, or C inertial axes of the molecule [4]. For H 2 O the symmetry axis corresponds to the B axis and the A axis lies in the plane of the molecule, so the ν 2 bend fundamental is a b-type band and the ν 3 asymmetric stretch is an a-type band [5]. For HDO where the symmetry is lowered by isotopic substitution, the ν 2 bend is now a mixed a/b-type band since the transition dipole has projections along both inertial axes.…”

“…Furthermore, HDO and H 2 O freely rotate in solid pH 2 such that at the low temperatures where solid pH 2 is stable, the overwhelming majority of HDO or H 2 O molecules populate only the lowest rotational level, namely a c K K J = 0 00 . Under these conditions, the rovibrational bands collapse into a single rovibrational transition which is b-type (1 11 ← 0 00 ) for the ν 2 bend and a-type (1 01 ← 0 00 ) for the ν 3 asymmetric stretch of H 2 O, but both b-and a-type rovibrational transitions are observed for HDO for the ν 2 and ν 3 vibrational fundamen-tals [5]. In this paper we show that satellite peaks are also present for the b-type rovibrational transitions of HDO, but due to the greater full width half maximum of the b-type transitions of HDO in solid pH 2 , the satellite peaks cannot be resolved from the monomer transition and thus are much more difficult to detect using FTIR.…”

Nuclear spin conversion of water inside fullerene cages detected by low-temperature nuclear magnetic resonance

“…The seminal case is that of H 2 , where the nuclear spin singlet state (I = 0) correlates with even rotational quantum numbers J (para-H 2 ), while the nuclear spin triplet states (I = 1) correlate with odd values of J (ortho-H 2 ). 1 Spin isomerism is also exhibited by many other small symmetrical molecules, such as water, [2][3][4][5][6][7][8][9][10][11][12][13][14] ethene, [15][16][17] and methane, [18][19][20][21] as well as freely rotating parts of a molecule, such as methyl (-CH 3 ) groups with low rotational barriers. [22][23][24][25] In many cases, the process of spin-isomer conversion, which requires a change in nuclear spin symmetry, is considerably slower than the spatial and nuclear spin transitions between quantum states of the same spin isomer.…”