Density functional theory (DFT) calculations of the structures, binding energies, vibrational frequencies and infrared intensities of methanol clusters containing two to five molecules have been carried out using the Becke3LYP functional. Thirteen representative H-bonded structures have been studied including cyclic, chain, branched-cyclic and branched-chain hydrogen bond structures. In the methanol trimer, tetramer, and pentamer, the cyclic structure is more stable by 3.5, 8.3, and 3.6 kcal/mol over the next most strongly bound minimum. In the tetramer and pentamer, the second-most stable minimum corresponds to a branched cycle. Chain structures are destabilized from the cyclic minimum by the loss of a hydrogen bond and from a smaller cooperative strengthening of the H-bonds that remain. In all branched structures studied, the formation of the branch H-bond strengthens the "branch-point" methanol's H-bond donation to its neighbor, but weakens its two acceptor H-bonds, leading to largely compensating effects on the total binding energy. The computed OH stretch vibrational frequency shifts (relative to the monomer at the same level of calculation) are used as points of comparison with recent experimental work on gas-phase (methanol) m and benzene-(methanol) m clusters and matrix-isolated (methanol) m clusters.

Resonant ion-dip infrared spectroscopy has been employed to record cluster-size-specific spectra of C 6 H 6-͑CH 3 OH͒ m with mϭ1-6 in the OH stretch fundamental region. The comparison of the spectra with the results of ab initio calculations on the pure methanol clusters enables the assignment of the hydrogen-bonding architecture in the clusters. In all cases, the methanol molecules aggregate together in a single subcluster. With mϭ1, a single infrared transition is observed, redshifted from that of a free methanol momomer by 42 cm Ϫ1 due to hydrogen bonding between benzene and methanol. The mϭ2 spectrum features two strong transitions at 3506 and 3605 cm Ϫ1. The lower frequency peak is redshifted from the free monomer value by 175 cm Ϫ1 and is assigned to the proton donor in the methanol dimer subcluster. The proton acceptor, which would be a free OH stretch in the absence of benzene, is redshifted by 76 cm Ϫ1 due to a strengthened hydrogen bond. In benzene-͑CH 3 OH͒ 3 , three sharp OH stretch transitions are observed at 3389, 3435, and 3589 cm Ϫ1. The comparison of these absorptions with ab initio calculations and with experiments on the pure methanol trimer leads to a structure for benzene-͑CH 3 OH͒ 3 which incorporates a hydrogen-bonded methanol trimer chain, confirming the earlier assignment based on its ultraviolet spectrum. The 3589 cm Ϫ1 transition, due to the hydrogen bond of the terminal methanol, is redshifted from the free monomer by 93 cm Ϫ1 , a value approaching that of the donor methanol in methanol dimer ͑Ϫ107 cm Ϫ1 ͒. The lower frequency transitions in the mϭ3 spectrum arise from the donor-acceptor and donor OH stretches in the methanol trimer chain. The spectral characteristics change when mϭ4. The OH stretch transitions are all located in a region around 3320 cm Ϫ1 and are significantly broadened compared to the smaller clusters. By comparison with ab initio calculations, the methanol tetramer structure in benzene-͑CH 3 OH͒ 4 is deduced to be a cyclic methanol tetramer. The spectra for mϭ5 and 6 are slightly redshifted but similar to mϭ4 and point toward cyclic structures as well.

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Resonant ion-dip infrared spectroscopy of benzene-(water) 9 : Expanding the cube The techniques of resonant two-photon ionization ͑R2PI͒, UV-UV ͑ultraviolet͒ hole-burning, and resonant ion-dip infrared ͑RIDIR͒ spectroscopies have been employed along with density functional theory ͑DFT͒ calculations to assign and characterize the hydrogen-bonding topologies of two isomers each of the benzene-͑water) 8 and (benzene͒ 2 ͑water) 8 gas-phase clusters. The BW 8 isomers ͑Bϭbenzene, Wϭwater͒ have R2PI spectra which are nearly identical to one another, but shifted by about 5 cm Ϫ1 from one another. This difference is sufficient to enable interference-free RIDIR spectra to be recorded. As with smaller BW n clusters, the BW 8 clusters fragment following photoionization by loss of either one or two water molecules. The OH stretch IR spectra of the two BW 8 isomers bear a close resemblance to one another, but differ most noticeably in the double-donor OH stretch transitions near 3550 cm Ϫ1 . Comparison to DFT calculated minimum energy structures, vibrational frequencies, and infrared intensities leads to an assignment of the H-bonding topology of the BW 8 isomers as nominally cubic water octamers of S 4 and D 2d symmetry surface attached to benzene through a H-bond. A series of arguments based on the R2PI and hole-burning spectra leads to an assignment of additional features in the R2PI spectra to two isomers of B 2 W 8 . The OH stretch RIDIR spectra of these isomers show them to be the corresponding S 4 and D 2d analogs of B 2 W 8 in which the benzene molecules each form a H-bond with a different dangling OH group on the W 8 sub-cluster.

To evaluate the incidence, risk factors, and outcome of central nervous system (CNS) recurrence in adult patients with non-Hodgkin's lymphoma, we evaluated 605 newly diagnosed patients with large-cell and immunoblastic lymphoma who participated in prospective chemotherapy studies. The Kaplan-Meier estimate of probability of CNS recurrence at 1 year after diagnosis was 4.5% (95% confidence interval [CI], 4.4 to 4.6). Twenty-four patients developed CNS recurrence after a median of 6 months from diagnosis (range, 0 to 44 months). In univariate analysis, an increased risk for CNS recurrence was associated with an advanced disease stage (P = .0014), an increased LDH (P = .0000), the presence of B-symptoms (P = .0037), involvement of more than one extranodal site (P = .0000), poor performance status (P = .0005), and B-cell phenotype (P = .008). Bone marrow involvement (P = .005), involvement of parenchymal organs (P = .03), and involvement of skin, subcutaneous tissue, and muscle (P = .002) were also associated with an increased risk for CNS disease. Multivariate logistic regression analysis identified only involvement of more than one extranodal site (P = .0005) and an increased LDH (P = .0008) as independent predictors of CNS recurrence. Established CNS recurrence had a poor prognosis. Only 1 of 24 patients remains alive and the Kaplan-Meier estimate of probability of survival at 1 year after the diagnosis of CNS recurrence is only 25.3% (95% CI, 6.9 to 43.7). Intrathecal treatment provided symptomatic benefit in only 1 of 6 patients. Radiation treatment provided symptomatic improvement in 6 of 9 patients treated. However, remissions were short and followed by systemic or CNS recurrence. Serum LDH and involvement of more than one extranodal site are independent risk factors for CNS recurrence in patients with large-cell lymphoma. The presence of both risk factors identifies a patient group at high risk for CNS recurrence. Established CNS recurrence can be rapidly fatal. Transient responses occur after radiation treatment.